22 



ELEMENTS OF BOTANY. 



Besides simple and compound leaves, there are other abnormal forms, 

 such as tendrils, spines, and pitchers, to which we can barely allude. 

 Tendrils (Fig. 32) and spines are but reduced leaves, while pitchers are 

 leaves which have undergone changes of structure to fit them for special 

 purposes, as for example, the entrapping of insects. 



Fig. 31.— A bi-pinnately compound leaf. 



Fig. 32. — Compound leaf of pea, with the terminal 

 leaflets changed to tendrils. The expanded leaflets at the 

 base are foliaceous stipules. 



As remarked above, a leaf may or may not have a distinct petiole. • In 

 the latter case the base of the blade is attached directly to the stem, with 

 or without an articulation. In all deciduous plants — that is, those whose 

 leaves fall away at the end of the growing season — the articulation is pres- 

 ent whether there be a petiole or not. In endogenous plants the articu- 

 lation is absent, the leaves, at the end of the growing season, dying away 

 gradually. 



In some cases where the petiole is absent, the base of the leaf encircles 

 or clasps the stem. Occasionally the leaf appears as though perforated by 



