ILLINOIS NATURAL HISTORY SURVEY MANUAL 1 



cells at the tip, called a root cap^ and discharging three principal 

 functions — anchorage, absorption of water and certain mineral 

 salts, and food storage. 



They may be grouped into two common systems — taproot 

 and diffuse. The taproot system is like that of the parsnip, 

 with a main central root extending vertically into the soil 

 and having many much smaller branches. In the diffuse root 

 system there are numerous roots of approximately equal size that 

 extend downward and outward in all directions. The majority 

 of diffuse-rooted plants have very fine ov fibrous roots, as corn 

 or other grasses, but some like asparagus and rhubarb have 

 many thick roots of diffuse arrangement. Roots of most flowering 

 plants are in the ground but in some instances they are aerial 

 or in water, and it is to be remembered that not all underground 

 structures are roots. 



Stems. — That portion of the plant that bears the leaves 

 is the stem^ and that place on the stem where the leaves are 

 normally borne is called a node. Also at the nodes, branch stems 

 are developed from the sides of the main stem. There are many 

 modifications of stems which at times are not easy to recognize; 

 of them the following will be met in the descriptions of plants 

 in this book: rhizome, tuber, bulb, corm, stolon, tendril and 

 scape. 



MODIFIED FORMS OF STEMS 



The rhizome or rootstock is an underground stem which is 

 usually elongated and horizontal. It grows from a terminal bud 

 and produces lateral buds at its nodes. A curious thing about 

 the rootstocks of perennials is that all of them in the same species 

 are found at approximately the same distance beneath the sur- 

 face of the soil. If in growing through the soil these underground 

 stems encounter a depression, they grow downward; if they 

 encounter an elevation they grow upward, so as to maintain 

 their usual distance beneath the surface. This phenomenon, 

 which is not well understood, is sometimes called the "law of 

 level." 



A fleshy underground stem, much enlarged and short, 

 usually ovoid or oblong, and also bearing a terminal and several 

 lateral buds, is called a tuber. The common potato is our best 

 example. 



A bulb is a short underground stem, tipped by a bud, from 



