SECT. I 



MORPHOLOGY 



43 



series of divergences, this is not usually suitable in the case of the foliar structures 

 of flowers and inflorescences, which have different puri^oses to serve. Other 

 relations of position also occur in the vegetative region, as has been shown by 

 GoEBEL (-•*), in particular in the case of dorsiventral shoots. The tips of 

 dorsiventral shoots are frequently coiled ventrally inwards, bearing their leaves 

 either dorsally or on the sides, but, in the latter case, approaching the dorsal 

 surface. The creeping stems of many Ferns or the flower-bearing shoots of 

 Forget-me-not [Myosotis] are 

 good examples of such dorsi- 

 ventral shoots. The line joining 

 successive leaves in such cases 

 is, at the best, but a zigzag. 

 On the ground of such observa- 

 tions as these it may be con- 

 cluded that the actual leaf- 

 arrangements represent adapta- 

 tions to definite conditions of 

 life, and that with alterations 

 in the latter other arrangements 

 must arise. 



The longitudinal distance 

 between the leaves of a shoot, 

 i.e. the length of the successive 

 internodes, also follows a definite 

 rule. According to Percy 

 Groom {^^) the lengths of the 

 internodes of the main axis of 

 a cormophytic plant most com- 

 monly increase at first and then 

 diminish. The lower the lateral 

 shoots stand on the main axis 

 the more closely do they corre- 

 spond with it in this rcsjiect. In 

 lateral shoots inserted higher 

 the region in which the length 

 of the internodes is increasing 

 tends to diminish and ulti- 

 mately the shoots may exhibit 

 only a succession of internodes 

 diminishing in length. Fio. 46.— Nepenthes roTjusta. (5 nat. size.) 



The Metamorphosis of Foliage Leaves. — The leaves of succulent 

 plants, in which the leaf-blade is more or less fleshy and thickened, 

 deviate from the typical form of a foliage leaf. Another striking 

 modification of foliage leaves is seen in peltate leaves, in which the 

 petioles are attached to the lower surfaces somewhat within the margin, 

 ^s in the leaves of the Indian Cress {2'ropaeolum majus, Fig. 187). In 

 the process of their development the young leaf-blades, in this case, 

 grow not only in the same direction as the petioles, as a prolongation 

 of them, but also horizontally in front of them. The tuljular leaves 



