242 PHYSIOLOGY. BOOK II. 



constitution : as in annual and herbaceous plants, and in those 

 the leaves of which are opposite and not alternate ; but all 

 the more essential circumstances of their growth are the same 

 as those of the apple tree. 



If we reflect upon these phenomena, our minds can scarcely 

 fail to be deeply impressed with admiration at the perfect sim- 

 plicity and, at the same time, faultless skill with which all the 

 machinery is contrived upon which vegetable life depends. A 

 few forms of tissue, interwoven horizontally and perpendicu- 

 larly, constitute a stem ; the development, by the first shoot 

 that the seed produces, of buds which grow upon the same 

 plan as the first shoot itself, and a constant repetition of the 

 same phenomenon, cause an increase in the length and breadth 

 of the plant ; an expansion of the bark into a leaf, within 

 which ramif^y veins proceeding from the seat of nutritive 

 matter in the new shoot, the provision of air-passages in its 

 substance, and of pores on its surface, enables the crude fluid 

 sent from the root to be elaborated and digested until it be- 

 comes the peculiar secretion of the species ; the conti'action of 

 a branch and its leaves forms a flower ; the disintegration of 

 the internal tissue of a petal forms pollen ; the folding in- 

 wards of a leaf is sufficient to constitute a pistil ; and, finally, 

 the gorging of the pistil with fluid which it cannot part with, 

 causes the production of a fruit. 



In hot latitudes there exists another race of trees, of which 

 Palms are the representatives ; and in the north there are 

 many herbs, in which growth, by addition to the ovitside, is 

 wholly departed from, the reverse taking place ; that is to say, 

 their diameter increasing by addition to the inside. As the 

 seeds of such plants are formed with only one cotyledon, they 

 are called monocotyledonous ; and their growth being from 

 the inside, they are also named endogens. In these plants the 

 functions of the leaves, flowers, and fruit are in nowise dif- 

 ferent from those of the apple ; their peculiarity consisting 

 only in the mode of forming their stems. When a monocoty- 

 ledonous seed has vegetated it usually does not disentangle its 

 cotyledon from the testa, but simply protrudes the collum and 

 the radicle ; the cotyledon swelling, and remaining firmly 

 encased in the seminal integuments. The radicle shoots 



