I wish it were possible to explain as elegantly as the original presents it, the ground-plan with each of its details nested in it, and that lucidity with which every part relates to every other, from that initial ‘flash’ I’ve expressed as: “Protectors of the ship.”
We must a slower way, de cap à pied; and this post being meant to illustrate that quality of mind which is our subject, most of the original discussion of the folio is omitted, having been (as it were) exegetical. Almost half this post is footnotes.
Swaying with a delicate balance on the height is a hatted figure with lower limbs ‘bent around’ – it is one of the Twins: the Dioscuri or Tindaridai  as the Greeks called them, but here the first and immortal brother Polydeuces is associated with Liber, as was done by the mysteries of Samothrace.  The form given the lower limbs alludes, simultaneously, to virtu in the elm, to the egg from which they were born, and to the lower of two lunar asterisms in Gemini, which constellation is everywhere associated with these Twins. By the Arabs the same asterism is called “the bent, or turned around” as Ib Majid explains in the fifteenth century. 
Here too we have the first clue to the plants’ identities, for as the figure appears bow-legged  and as Liber “clings to the high elm”  so elm-wood’s being famously pliant had it sought-after by bowyers. The archer was a ship’s chief defence, and so bow and arrow another attribute of the Dioscuri. This figure’s balancing as if in a high wind, seeming to hold fire in its hands reminds us too that Liber’s harmless ‘lightning' – was ever a good omen for the storm-tossed ship, when all other lights were extinguished:
Leaping on the peaks of their well-benched ships,
brilliant from afar as you run up the fore-stays,
bringing light to the black ship
in the night of trouble.
from: Alcaeus’ Hymn to the Dioscuri, trans. Alexander Nikolaev.
Just so this flameless light is sometimes called “harbour fire” still, though we call it St.Elmo’s fire, he the patron of Formio, named Hormiae (good harbour) by the Greeks.
Another form of ‘need fire’ comes again from the elm; made by its wood as fire-drill often miscalled a ‘dowel'. The figure’s hands are formed as if twirling small fire-sticks and (though this last may be co-incidental) are drawn overall in a way suggesting the pomegranate flower, the Phoenicians’ emblematic ‘lily’.
On folio 5v, the pair are correctly provided with their star-topped caps  telling us that the maker was naturally familiar with the older forms of image. The two examples shown below are from the last phase of Hellenistic rule in the Mediterranean.
This second century BC is also when the earliest of the eastern Greek works were written from which passages were taken and included in the Anicia Juliana codex, where we also find a ‘template’ layout very common among botanical folios of Beinecke MS 408. (The point was discussed here.)
Distance between Gemini’s two head stars (α and β Geminorum), was taken as a standard measure by navigators of land or sea, and was reckoned an ell’s length – that is, the length of an average clothyard shaft or a weaver’s beam: about 28 inches. In modern terms the distance is measured as 4½ °.
An earlier Hellenistic coin (above) shows the Dioscuri with the arrow-shaft; its length being approx. 30 inches, that of the Greek ‘step’, the haploun bēma (ἁπλοῦν βῆμα), and two made the pace. The Arabs also called the asterism formed of α and β Geminorum: al Dhira’: “the ell-length”.
In folio 5v, the relative distance between these two, and the slight difference in elevation reveals the first enunciator’s entire ease with these matters: the Greek context; Hellenistic forms; the parallel botanical, cultural and astronomical matter. While I daresay those determined on a theory of all-Latin medieval or ~renaissance origin for these images might attempt an argument about it as an allegorical or mnemonic construct of medieval European type, I could not begin to agree. It comes down to that ‘cast of mind’. This image is so easily and effortlessly done. More to the point, it is so effortlessly conceived and its purpose (as we’ll see) is not literary, nor is it allegory, but absolutely and utterly practical. As a whole, the image is a sort of shopping list of products gained from the plants in this group – it’s not about the Dioscuri, but about the economic and practical worth of plants and matter associated with them. It simply happens that, for the first enunciator, the Dioscuri were the ‘second nature’ association for this diverse but related set of items, whose single theme (as we’ll see later in more detail) are materials serving to ‘protect the ship’. But it is significant that he supposed these hats as high-crowned and star-topped in a way characteristically eastern Mediterranean and Hellenistic.
All the compositional elements I’ve mentioned so far were part of that “ground-plan perceived in a flash” – to use Kitto’s words again. There’s nothing heavy, nothing forced or laboured in the enunciation even if, necessarily, in the present exposition. For all its complexity, the image remains simple; its design perfectly lucid. We can only be grateful that the 15thC copyists (and all before them) were so faithful to the original.
The Dioscuri were, of course, the quintessential “Protectors of the ship” having been conferred power over wind and waves:
sailors when caught in storms always direct their prayers to the deities of Samothrake (Samothrace) and attribute the appearance of the two stars [α, β Geminorum] to the epiphany of the Dioscuri.
Diodorus Siculus, Bibliotheca Historica, Book 4.43.2
… continued ….
 The English word ‘tinder’ may be suggested by the image so I thought I might mention that etymology evolves, like any other science. The habit of the eighteenth- and nineteenth-century etymologists was to derive almost everything in English from Latin or German, but in this case the latest view is: “Old English tynder, related to tendan “to kindle”, from Proto-Germanic *tund- “ignite, kindle.” In other words that the German, like Dutch, Swedish or Norse terms are related but less directly than formerly thought.
 Pliny the Elder, Natural History 6. 78 (trans. Rackham) : “Most people assign to India the city of Nisa and Mount Merus which his sacred to father Liber [Dionysos], this being the place from which originated the myth of the birth of Liber [Dionysos] from the thigh of Jove [Zeus].” But the Homeric hymns and other older sources show this an error. The original Liber, the first Dionysius, was Egypto-Phoenician. The first Homeric Hymn to Dionysus, dated 7th-4thC BC has: “[Zeus] gave you birth remote from men and secretly from white-armed Hera. There is a certain Nysa, a mountain most high and richly grown with woods, far off in Phoinike, near the streams of Aigyptos…” Homeric Hymn 1 to Dionysus (trans. Evelyn-White). The ‘first Dionysos’ was Sabazios, or Zagreus. A good online site for the myths and sources are an excellent pair of blogposts at Spacezilotes, a wordpress blog: “Metis Menis of Dion Ysus (A) (15th. Feb. 2013) and … (B), (1st. May 2014).
[3.] ‘al-Han’a. This rises at dawn after the 221st day of the [Persian] year and it is a windy and good-omened group. It consists of stars formed like the letter n ( ن ) and it is given this name because it is bent round, i.e. its ends come together as the Arabs say hana’at, i.e. some such thing is bent or turned around, meaning that part of it is turned round towards another part. There are no well-known stars in it except one which is called al-Maisān of the third magnitude..’ Kitāb al Fawā’id.. (Tibbetts’ translation pp.88-89). In Ibn Majid’s system, according to Tibbetts, al-Han’a consists of ε,γ,ζ,λ,δ Geminorum. (op.cit., p. 552).
 The term used by the Greeks of pre-Roman times is uncertain. The Roman term blaesus means “curved legs” and while its etymology derives it from the Greek βλαιiσóς, Simon and Steger ( Sudhoffs Arch.  Vol. 95, No.2, pp. 209-221) point out that the Greek does not mean quite the same.
 “Liber…” A visual/verbal pun – deliberate, I think. So, Isidore quotes Virgil concerning the elm’s bast fibre, writing “Liber is the inner membrane of bark, which clings to the wood. With regard to this, Virgil thus: The bark (liber) clings to the high elm“. I cannot think the medicinal Slippery Elm meant; Ulmus rubra is an American species. Perhaps Timperly is correct, connecting the word to the Latin word for a book – initially a type was made of the inner bark (bast fibre) – though he refers to Europe’s use of the lime tree not the elm, while referring to the Egyptians having used the elm among other trees for the same purpose. I regret being unable to spare time to consult more recent sources on this last point. (Timperly, The Dictionary of Printer and Printing (1839) p.22.
 The elm’s wood bends well … making it quite pliant. …Elm is also prized by bowyers; of the ancient bows found in Europe, a large portion of them are elm. During the Middle Ages elm was also used to make longbows if yew was unavailable. The … trunks were favoured as a source of timber for keels in ship construction (in medieval Europe). – from a wiki article ‘Elm’.
I omitted other allusions here though they were probably known to the first enunciator and could be relevant e.g., an inference might taken that the mariner’s entry into the Erythrean Sea was equated at that time with descent into the underworld. Homer tells us that elms were planted by nymphs over the underground tomb of Eetion, king of Trojan Thebes slain by Achilles; the Metamorphoses tells of the nymph Erytheia becoming an elm (Ptelea); and the Roman Virgil has the spirits of dreams (Oneiroi) perch in an elm at the entrance of Hades.
 Liber [Zagreus] was identified with Polydeuces. Debate continues among scholars over the origin of this ‘first’ Dionysius, but opinion tends towards a Phoenician origin and identification in the first instance with Zabazios. The issue need not concern us. The point is that Zagreus, another son of Zeus, was famously permitted to play childishly -i.e. harmlessly – with his father’s lightning.
 Richen says that “It was probably the toughness of wood which led to the elm being used for production of fire by drilling [in many parts of the older world]” and that the ancient practice survived to recent times in Europe ” as a ritual performance, for the generation of need-fire”. R.H. Richens, Elm, C.U.P 1983 (pp.109-9).
 As it is often used, but invariably described in archaeological reports. The University College, London (here) notes it found in “wide use in ancient Egypt, most often smaller objects such as dowels” with an additional note that it is “tough and durable when permanently wet”. Whether it like salt-water spray as much, I’ve not determined.
 “During the voyage of the Argonauts .. when the heroes were detained by a vehement storm, and Orpheus prayed to the Samothracian gods, the storm suddenly subsided and stars appeared on the heads of the Dioscuri” For the source texts see Smith’s Dictionary of Greek and Roman Biography and Mythology, Vol. 1, p.1053. online.