10 



PART I. MORPHOLOGY. 



[6 



become separated from the member bearing them, and fall off after 

 a time, when they are said to be deciduous. Leaves are nearly 

 always deciduous. In most perennial plants the foliage-leaves all 

 fall off at some season of the year, which, in temperate climates, is 

 the autumn. But in " evergreen " trees and shrubs, the leaves, 

 which may last for more than one year, do not all fall off at once. 

 Those parts of the plant which are connected with reproduction 

 are especially deciduous: for instance, the leaves forming the 

 perianth of the flower, sometimes the whole inflorescence (e.g. 

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



member thus falls off it 

 leaves a more or less per- 

 manent scar : the scar which 

 marks the position of a 

 fallen leaf is a leaf-scar. 



Hairs and reproductive 

 organs are generally de- 

 veloped as lateral out- 

 growths upon the members, 

 but they are occasionally 

 developed directly from the 

 growing-point. They are 

 usually developed from one 

 or more superficial cells, but 



\V \lfllllllffill / / in s me cases the dee P er 

 ^PIllIP^ / / layers of cells also take part 



in their formation. 



All lateral members may 

 be developed either singly 

 or several together at the 

 same level on the parent 

 member. When in any cross-section of the parent member not 

 one only, but two or more lateral members occur at the same level, 

 they are said to form a ivhorl ; for instance, of secondary roots 

 round a parent root, or of leaves round a stem as in Herb Paris 

 (Paris quadrifolia). The members of a whorl may be developed 

 either simultaneously, or one after the other ; hence a whorl may 

 be either simultaneous or successional. Members not developed 

 in whorls are said to be scattered. 



6. The Arrangement of the Lateral Members. The 

 arrangement of the leaves on the stem is most intimately con- 





Fio. 3. Diagrammatic longitudinal section 

 through the growing-point of a stem: b the 

 leaves; fcn their axillary buds; e epidermis; 



vascular bundles. 



