GROWTH BY THE STEM. 23 



grow into a spherical figure. Pressed upon, how- 

 ever, by the surrounding earth, impelled upwards by 

 the current of sap ascending from the root, and 

 attracted into the air by the necessity it feels of respi- 

 ration, the young stem assumes a cylindrical form, its 

 sides having a tendency to solidify, and its point 

 to grow longer. This point, or plumule, or first leaf- 

 bud, soon attracts to itself the food which the root 

 procures from the earth, and a part .of the nutritive 

 matter which is stored up in the seed-leaves. It feeds 

 especially upon the latter until the store is exhausted, 

 and by the time this happens it is clothed with leaves, 

 which are themselves able to feed it after the seed- 

 leaves have perished. In brief, the stem is a branch 

 produced by the first leaf-bud which the embryo 

 plant possesses. 



43. When the stem is first called into existence, it 

 is merely a small portion of cellular tissue : an organic 

 substance, possessing neither strength nor tenacity, 

 and altogether unsuited to the purposes for which 

 the stem is destined. If such matter formed exclu- 

 sively its solid contents, the stem would have neither 

 toughness nor strength, but would be brittle like 

 a mushroom, or like those parts of plants of which 

 cellular tissue is the exclusive component ; such, for 

 example, as the club-shaped spadix of an Arum, of 

 the soft prickles of a young Eose branch. Nature, 

 however, from the first moment that the rudiment of 

 a leaf appears upon the growing point of a stern, , 

 occupies herself with the formation of woody matter, 

 consisting of tough tubes of extreme fineness, which 



