CLASSIFICATION OF LEAVES: DURATION 



81 



tire (Fig. 388), or, upon the other hand, 

 cortex and epidermis may, at the end and 

 for a variable distance toward or even to 

 the base of its branch system, be separate 



Leaves, considered in the gn^«*» are to 

 be classified as to duration, their reten- 

 tion upon the phint, texture, surface, at- 

 tachment to the stem, attachment of the 



from its neighbors, thus making a mar- blade to the petiole, form, including gen- 

 eral outline, special form of bnse and of 

 apex, venation, margin, division, modi- 

 fication of form and function. 



As to duration leaves are Annual and 

 the trees producing them Deciiluous, 

 whoa their duration is through a single 

 season only, and Evergreen, when thoy 

 remain in their normal and active condi- 

 tion into the succeeding season. Ever- 

 green loaves may be either biennial, the 

 ordinary form, or perennial. Persistent 

 leaves are those which remain upon the 

 tree, but in a dead condition, until forced 

 ofif by the growth of the following senson. 



As to their texture and consistency, the 

 ordinary form of leaf, In which it pos- 

 sesses active chlorophyll tissue, is denom- 

 inated Herbaceous, in contradistinction 

 to the Scarious or Scariose form, in which 



gin more or less toothed, lobed or divided. 

 When the division is thus carried entirely 

 to the point of origin of such branch sys- 

 tem, the lamina of the latter may still be 

 connected at its base with the midrib, or 

 it may be entirely separate from that also, 

 so that the connection of that branch 

 system with the rest of the leaf will be by 

 its principal vein only (Fig. 391, &c.). An 

 articulation will then form there, and the 

 lamina will consist of a number of dis- 

 tinct blades of secondary rank, thus giv- 

 ing us the Compound Leaf. These sec- 

 ondary blades may be similarly divided, 

 giving us the Decompound Leaf. The di- 

 visions of a compound and decompound 

 leaf are called Leaflets, and are subject 

 to the same conditions, description, and 

 classification as primary leaves. Decom- 

 pound leaves are spoken of as once com- 

 pound, twice compound, and so on. Sti- 

 pules, called Stipellae (Fig. 391a) may de- 

 velop at the base of leaflets, but buds do 

 not form there, a distinction which is 

 sometimes useful in determining whether 

 a body is a branch, bearing simple leaves, 

 or a compound leaf. The continuation of 

 the petiole throughout the blade of a com- 

 pound leaf, is called its Rhachis (Fig. 

 391b). 



it has a dry and papery texture. Herba- 

 ceous leaves are Membranaceous in their 

 ordinary form, that is, not excessively 

 thickened, Coriaceous when tough and 

 leathery, Fleshy « or Succulent when 

 largely parenchymatous, thickened find 

 juicy. A leaf which exhibits translucent 

 dots when held against a strong light is 

 called Punctate. The surfaces of leaves 

 may be classified in two ways, first, as to 

 the characteristics of the individual tri- 



*. 



