58 



THE ORGANS OF PLAOTS. 



The Stem. In all flowering plants the stem proceeds from the seed and that part 

 of it termed the plumule ; whilst, at the same time, the root is developed from another 

 part of the same seed viz., the radicle. These two newly- formed organs thence assume 

 diverse directions, the root passing downwards to fix the plant firmly to the earth, and 

 to abstract nutriment from the ground ; whilst the stem usually emerges from the soil, 

 and grows in a perpendicular direction, so as to bear the leaves and other organs of 

 growth and reproduction from the ground, and expose them freely to the action of the 

 light, air, and moisture. The point in the seed whence the stem and root diverge is 

 known as the collum or neck (Fig. 100 i), and even in trees which attain to a consider- 

 able size this line remains more or less distinct. 



When the seed has begun to germinate, and the growing points just referred to have 

 lengthened, the other parts of the seed viz., the cotyledons, or seed-leaves, enlarge, and 

 take on the function of nutrition by converting the starch contained within them into 

 sugar. At length, by their elongation, they emerge from the soil, and appear as two 

 opposite roundish leaves, which are capable of absorbing 

 oxygen from the air, and fixing carbon within the tissues 

 which are then in process of formation. At this stage, 

 then, we find a root, stem, collum, and seed-leaves, all of 

 which are represented in'Fig. 103. 



The current of sap having been set in motion by the 

 action of the cotyledons, or seed-leaves, the latter disappears, 

 and the plumule, or young stem, continues to elongate 

 rapidly, and until it arrives at the point whence its first 

 leaf is to issue, is technically termed a node. At this point 

 the stem swells, and the structures of which it is composed 

 are bent out of their former direction, and, in part, enter 

 within the structure of the newly-developed leaf. The 

 stem may now fairly take on the term of ascending axis, 

 which is usually given to it, since it has begun to develop 

 the organs which are subsequently to be arranged around 

 it as their centre. It has also received a variety of other 

 names, which it may be useful to mention viz., the cau- 

 dex intermedius and ascendens, truncus or truncus as- 

 cendens, with culmus and stipes. All these have a similar 

 signification. 



The growth is not arrested by the development of a 

 node and leaf, but proceeds for a certain period, until ano- 

 leaves7wh7clTave' appeared ther leaf and node are formed ; and so on progressively 



point of the stem, elongated then a scries of nodes and spaces between them, which 

 Det ^thVcollumf s e e ( p a 1 I : ating (or s P aces are termed internodes. A stem may thus be said to 

 rather connecting-) the part of consist of a number of nodes, with their internodes. 

 KS^^^rtbTm Nodes.-These are well seen, in all grasses, as the 

 it, the descending axis. ordinary grass of this country; with wheat, oats, and other 



grasses ; and more particularly in the bamboos and canes 

 of southern climes. It is there found as a distinct bulging 

 around the stem, of a hard and rounded character, and oftentimes bending the stem 

 from the perpendicular direction. Ifi wooded plants, or trees, in general, it is less per- 



Fig. 103. Exhibiting the parts 

 of a plant soon after the com- 

 mencement of germination. 

 c, the cotyledons, or geed- 



d, the radicle, with the root- 

 lets proceeding from it. 



