22 



PART I. THE MORPHOLOGY OF PLANTS. 



[3. 



(e.g. Cardamine pratensis), or, more commonly, from stems, some- 

 times from the growing-point of the stem (e.g. Isoetes, Angio- 

 pteris, etc.) ; they are usually of endogenous origin, but some- 

 times of exogenous (e.g. Nasturtium ojficinale, Gardnmine pratensis, 

 Neottia Nidus-Avis, Pbylloglossum, Lycopodium cernuum). 



In some few cases, the segmentation of a member into similar members, 

 takes place neither by lateral nor by dichotomous development, but by an alto- 

 gether peculiar process. For 

 instance, a portion of the full- 

 grown thalloid shoot of some 

 Laminarieae is segmented into 

 similar members. To begin 

 with it is unsegmented; but 

 it gradually splits, by degener- 

 ation of rows of cells, into seg- 

 ments which remain united 

 only at the base. The same 

 thing occurs in the leaves of 

 some Palms and Aroids (e.g. 

 Philodendron). 



The members when 

 once formed commonly 

 persist ; but frequently 

 they become separated 

 and fall off after a time, 

 when they are said to be 

 deciduous. The most 

 common instance is that 

 of foliage -leaves. In 

 most perennial plants 

 the foliage-leaves all fall 

 off in the autumn ; but 

 in some the evergreen 

 trees and shrubs the 

 leaves, which may last 

 for more than one year, 

 do not all fall off at the 

 same time. Those parts of the plant which are connected with 

 reproduction are especially deciduous; for instance, shoots which 

 subserve vegetative reproduction, the leaves constituting the peri- 

 anth of flowers, sometimes the whole inflorescence (e.g. catkin), 

 sometimes the fruit (e.g. cherry), seeds, etc. When a member 



FIG. 10. Lamina-rid digitata (after Harvey ; much 

 reduced). The intercalary growing-point is situated 

 at the junction of the old frond (6) with the new frond 

 () ; a is gradually splitting into segments. 



