106 STRUCTURAL BOTANY. 



Thistle and Horse-nettle. Leaves may also be armed with 

 stinging hairs which are sharp and tubular, containing a poison- 

 ous fluid, as in Nettles and Jatropha stimulans (503). 



314. A pruinous surface is covered with a bluish-white waxy 

 powder, called bloom, as in the Cabbage ; and a punctate leaf 

 is dotted with colored points or pellucid glands. 



315. In texture leaves maybe membranous, or coriaceous 

 (leathery), or succulent (fleshy), or scarious (&YJ}, rugous (wrin- 

 kled), etc., which terms need only to be mentioned. 



316. Double terms. The modifications of leaves are almost endless. Many other 

 terms are defined in the glossary, yet it will often be found necessary in the exact descrip- 

 tion of a plant to combine two or more of the terms defined in order to express some in- 

 termediate figure or quality ; thus ovate-lanceolate, signifying a form between ovate and 

 lanceolate, etc. 



317. The Latin preposition sub (under) prefixed to a descriptive term denotes the 

 quality which the term expresses, in a lower degree, as subsessile, nearly sessile, subser- 

 rate, somewhat serrate. 



Review. 300. How a simple leaf may become compound. 301. What are the leaflets ? 

 The petiolules ? The rachis ? 302. Describe the pinnate leaf. What sort is fig. 356 ? 

 357 ''. .358 ? 303. Numbers of leaflets ? In trifoliate ? In binate ? What of the Lemon 

 leaf? What is bipinnate? Tripinnate? Decompound ? What singularity in the leaf 

 of Honey-locust ? Define a biternate leaf. A triternate. Distinguish palmately and jrin- 

 valely ternate. What kind of leaf-form is fig. 355 ? 359 ? 365 ? Name and define the 

 acuminate, and other forms of leaf-points. What leaf is truncate ? Emarginate ? etc. 

 30!). Speaking merely of the margin, when is it entire? Dentate ? Serrate? Crenate? 

 What if the teeth are fine ? Doubly serrate ? 310. Undulate ? Erose ? Crisped ? 312. 

 As to surface, what is glabrous ? Scabrous? With a dense coat of hairs, mention six 

 modifications. Distinguish hirsute Pilous Hispid. Also setous, spinous. 311. What 

 covers the pruinous surface? Explain such terms as ovate-lanceolate. Use of sub 9 

 Explain fig. 388, 389, 390. 



CHAPTER XXIII. 



TRANSFORMATIONS OF THE LEAF. 



318. Hitherto we have considered the leaf as foliage merely 

 constituted the fit organ of aeration by its large expansion of 

 surface. This is indeed the chief, but not the only aspect in 

 which it is to be viewed. The leaf is a typical form ; that is, a 

 type, or an IDEA of the Divine Architect, whence is derived the 

 form of every other appendage of the plant. To trace out this 

 idea in all the disguises under which it lurks, is one of the first- 

 aims of the botanist. Several of these forms of disguise have 

 already been noticed for example : 



311). The scales which clothe the various forms of scale- 



