456 BOTANY. 



healthy. These annual rings or layers, however, it may be re- 

 marked, are not always exactly concentric around the medullary 

 canal. The layers are thickest on the sides from which the 

 roots derive most nourishment ; and the northern side of many 

 trees, being less exposed to heat, is often found less dilated. 

 In this manner do the larger vegetables increase in size much 

 beyond all the other portions of organized nature. The cele- 

 brated Chestnut of Mount Etna, 173 feet in circumference, has 

 in the hollow of its trunk a cabin of seven paces broad, and 

 eight in length and height ; and Pliny mentions a platanus in 

 Lycia, in the hollow trunk of which the Roman Consul Lucia- 

 nus with twenty of his followers supped and slept. 



The roots of plants are more or less furnished with radicles, 

 distributed around the main root, and extending in the soil, their 

 tendency being always downwards, as the stem and leaves on the 

 contrary seek the light. There are plants, however, all root, as 

 the truffle ; others seem to have scarcely any, as the Algce, ab- 

 sorbing their nourishment by the leaves alone. Some attach 

 themselves by a series of roots, as the ivy, to the stems of other 

 plants, or by a single attachment, as many species of Fungi. The 

 Lemnce have floating roots ; and many plants develope at their 

 roots tubercles more or less large, as the potatoe. The Cacti 

 and other fleshy plants live so little by their roots, that they 

 vegetate in arid sands. Bulbous roots, as the onion, are to be 

 considered as the rudiments of the stems to be developed in fu- 

 ture years. 



The different kinds of stems or trunks of plants have receiv- 

 ed various names according to their structure. These are, the 

 stem (caulis), peculiar to herbaceous plants ; the trunk (trun- 

 cm), proper to shrubs and trees ; the straw (culmus), appro- 

 priated to grasses ; and the scape or stalk (scapus) which dif- 

 fers from the others in bearing only flowers. The stem is simple 

 or branched, naked or leafy, straight or flexuous. The pedun- 

 cles are divisions of the stem supporting the organs of fructifica- 

 tion either in a head, a spike, a catkin, or in a corymb, an um- 

 bel, panicle, &c. The branches afe of the same organization 

 as the stems of which they are divisions, and they for the most 

 part correspond in size to the roots which nourish them. 



The leaves of plants are generally in the form of flattened ex- 

 pansions, of which the upper side is greener and more polished 

 than the lower surface, which is porous and unequal. They 



