. On the relation of phyllotaxis to mechanical laws. Phyllotaxis; Leaves. 254 RELATION OF PHYLLOTAXIS TO MECHANICAL LAWS. have been wholly withdrawn from the testa and are beginning to expand, present a very remarkable appearance (fig. 86, XL, III., IV.). Parastichies are still wanting, as indicating any definite system, and the primordia assume irregular forms under pressure ; so that the resem- blance to a section of ordinary packed parenchyma is very close. Growth continues to be irregular in the individual primordia (III.), but as the plants become older it appears more regular and parasti
. On the relation of phyllotaxis to mechanical laws. Phyllotaxis; Leaves. 254 RELATION OF PHYLLOTAXIS TO MECHANICAL LAWS. have been wholly withdrawn from the testa and are beginning to expand, present a very remarkable appearance (fig. 86, XL, III., IV.). Parastichies are still wanting, as indicating any definite system, and the primordia assume irregular forms under pressure ; so that the resem- blance to a section of ordinary packed parenchyma is very close. Growth continues to be irregular in the individual primordia (III.), but as the plants become older it appears more regular and parastichies begin to appear. How far these appearances are partly due to ir- regularities in the phyllotaxis system itself is thus obscured ; but the irregularity in the phyllotaxis is associated with irregularity in the shape of the members. That the phyllotaxis system is itself irregular is rendered probable by the comparison of other types (Cedrus Atlanti- cus), but this would not necessarily lead to irregular shapes in the members. As the contact-parastichies become increasingly obvious, they give very anomalous results: for example, (IV.) is apparently a system (6 + 1) with irr^ular packing among the first leaves; but when the cotyledons fully expand, and the plumule becomes visible between them, the presence of a definite system of the normal series becomes clear for the first time. The central portion of the bud is now unmistakably (5 + 8) (V.), although in the example figured this appears to have been only rendered normal by the opening up of a new curve by the member numbered 1. Seedlings vary from (5 + 8) to (6 +10), (5 + 8) being the usual type. Section of a plant in which the primary shoot had reached the length of 6 inches, shows a normal (5 + 8) system with remarkable perfection, the members retaining to a v6ry considerable degree the form of the quasi-square of the theoretical con- struction, owing to the very small extent to which progressive bilater- ality has been c
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