198 



THAT'S IT; 



558. 



In general, roots extract from 

 the earth substances which con- 

 tribute to the growth of the 

 plant. But all parts of the root 

 do not equally perform this office, 

 which is accom- 

 plished chiefly, if 

 not solely, by the 

 extremities of the 

 small fibres, that 

 are terminated by 

 little spongy 

 bodies called 

 spongioles, 19. 

 These may be 

 seen by the aid 

 of the microscope, attached as 

 little bags to the minute fibres 

 of the roots. 



Roots are not only absorbing organs, they 

 excrete matters useless or injurious to the 

 plant, and the soils in which they have long- 

 grown become charged with the substances thus 

 excreted. An experiment was made upon a 

 plant, the root of which was divided, and one 

 part of it placed in a solution of sugar of lead, 

 the other in a glass of pure water. The branch 

 immersed in the solution of lead absorbed the 

 poison, the other branch excreted it into the 

 pure water. This explains the practice of 

 rotation of crops in agriculture; the rotation 

 being required on account of the excretions of 

 a plant being injurious to itself, but beneficial 

 to other kinds, as the excretion of one plant 

 is the food of another. 



Botanists employ different 

 terms to distinguish the kinds of 

 stems or stalks that support the 

 leaves, and the organs of fructifi- 

 cation. These are, the stem, 

 which is considered peculiar to 

 herbaceous plants ; the trunk, 

 which is proper to shrubs and 

 trees ; the stipe, which is the 

 stem of endogenous plants, such 

 as palms, bamboos, canes, &c, 

 a cylinder of equal thickness 

 from top to bottom, sometimes 

 swelling out in the middle or the 

 top, branchless, but crowned at 

 the summit with a tuft of leaves 



and flowers ; the culm, or strair 

 which is the stem of the grasses ; 

 and the stalk, which is applied to 

 the supports of those plants that 

 bear flowers only. 



Some of the simple plants 

 have no stem, as the lichens, 552 ; 

 others have a soft herbaceous 

 mass, in which are combined 

 stem, branches, and leaves. In 

 the fungi, the nature of the stem 

 is simple, and composed of cel- 

 lular membrane, like the other 

 parts of the plant. 



The stems of herbaceous plants 

 are of two kinds : those that are 

 subterranean, extending below the 

 surface of the earth ; and those 

 that are aerial, growing above it. 

 Herbaceous plants are such as 

 perish annually down to the 

 underground stem — soft succulent 

 vegetables ; herbaceous stems are 

 soft, not woody. The subterra- 

 nean stems are such as those of 

 the potatoe, onion, beet, parsnip, 

 turnip, &c. The roots of these 

 plants are fibrous branches thrown 

 off from the underground stem. 



Aerial stems consist of five 

 kinds : the sucker, the vine, the 

 root-stock, the runner, the off-set 

 and the imperfect bulbs of orchi- 

 daceous plants. 



Woody trunks are those which 

 belong to shrubs and trees ; they 

 are divided into two classes : 

 such as grow from their outside, 

 exogenous — and such as enlarge 

 from within, endogenous. 



The exogenous * plants com- 

 prise the largest primary class in 

 the vegetable kingdom. As long 

 as they continue to grow, they 

 add new wood to the outside of 



* From two Greek words meaning* to Droduce witbout. 



