EXPLANATION OF TERMS 7 



In a district like ours, where the topography is exceedingly 

 diverse, the number of combinations in which external factors 

 may unite to influence the appearance of the vegetation is very 

 great. The number of species represented is therefore large and 

 the variation within each species is often considerable. The 

 detailed study of such modifications and their causes is one of the 

 most promising fields of botanical research and it would be diffi- 

 cult to find better opportunities for these studies than are afforded 

 in the Yosemite National Park. 



EXPLANATION OF TERMS. 

 The descriptions in this Flora are, in the main, couched in 

 clear and readily intelligible language. For purposes of accuracy, 

 however, it is often necessary to use terms which are familiar 

 only to botanists. For the guidance of others, the following brief 

 outline has been prepared, which, used in connection with the 

 glossary just preceding the index, should fully equip any intelli- 

 gent student for the successful and pleasurable use of this book. 

 Special terms used entirely or mostly in a single family of plants 

 will be explained in the family descriptions. 



The Root and Root-like Organs. 

 The root ordinarily grows downward from the base of the stem, 

 forks and spreads in the earth, absorbing food and water for the 

 plant. Fibrous roots have slender, thread-like branches. Tap- 

 roots are single strong roots that descend perpendicularly, with 

 few branches. Rootstocks are underground, horizontal, root-like 

 stems, usually rooting at the joints and sending up leafy stalks. 

 The rootstocks of ferns produce fronds instead of leaves. Bulbs 

 are thickened underground bodies made up chiefly of fleshy leaves, 

 as in the Onion. They may be scaly, as in the Lilies, or with a 

 fibrous coat, as in the Soap-root. 



The Stem. 



The stem grows upward from the root and bears buds which 

 grow out into leafy branches. It finally produces flowers and 

 fruit. 



Stems are of two types. In Endogens the woody portion occurs 

 in small bundles or fibers, which, in cross-section, are seen to be 

 distributed throughout the stem. In Exogens the woody system 

 grows in annual concentric layers between a central pith and an 

 exterior bark, so that in cross-section we see a series of rings of 

 wood, or in the first year one ring, surrounding the pith and sur- 

 rounded by the separable bark. Endogenous stems produce leaves 

 with parallel veins, while leaves on exogenous stems are nearly 

 always net-veined. 



