Fig. 45. Cycas pectinata: circumnutation of young leaf whilst emerging from the ground, feebly illuminated from above, traced on vertical glass, from 5 P.M. May 28th to 11 A.M. 31st. Movement magnified 7 times, here reduced to two-thirds of original scale. Canna Warscewiczii (Cannaceae).—A seedling with the plumule projecting one inch above the ground was observed, but not under fair conditions, as it was brought out of the hot-house and kept in a room not sufficiently warm. Nevertheless the tracing (Fig. 46) shows that it made two or three incomplete irregular circles or ellipses in the course of 48 hours. The plumule is straight; and this was the first instance observed by us of the part that first breaks through the ground not being arched. Fig. 46. Canna Warscewiczii: circumnutation of plumule with filament affixed obliquely to outer sheath-like leaf, traced in darkness on horizontal glass from 8.45 A.M. Nov. 9th to 8.10 A.M. 11th. Movement of bead magnified 6 times. Allium cepa (Liliaceae).—The narrow green leaf, which protrudes from the seed of the common onion as a cotyledon,[4] breaks through the ground in the form of an arch, in the same manner as the hypocotyl or epicotyl of a dicotyledonous plant. Long after the arch has risen above the surface the apex remains within the seed-coats, evidently absorbing the still abundant contents. The summit or crown of the arch, when it first protrudes from the seed and is still buried beneath the ground, is simply rounded; but before it reaches the surface it is developed into a conical protuberance of a white colour (owing to the absence of chlorophyll), whilst the adjoining parts are green, with the epidermis apparently rather thicker and tougher than elsewhere. We may therefore conclude that this conical protuberance is a special adaptation for breaking through the ground,[5] and answers the same end as the knife-like white crest on the summit of the straight cotyledon of the Gramineæ. After a time the apex is drawn out of the empty seed-coats, and rises up, forming a right angle, or more commonly a still larger angle with the lower part, and occasionally the whole becomes nearly straight. The conical protuberance, which originally formed the crown of the arch, is now seated on one side, and appears like a joint or knee, which from acquiring chlorophyll becomes green, and increases in size. In rarely or never becoming perfectly straight, these cotyledons differ remarkably from the ultimate condition of the arched hypocotyls or epicotyls of dicotyledons. It is, also, a singular circumstance that the attenuated extremity of the upper bent portion invariably withers and dies. [4] This is the expression used by Sachs in his ‘Text-book of Botany.’