ASSIMILATION. 113 



then that its growth ceases. The ostiole is, therefore, not 

 the point by which the grain of starch is attached to the 

 walls of the cell, but it is the cicatrice of the canal by 

 which the matter which formed the successive layers pene- 

 trated, in a state of solution.* 



Physiologically considered, starch is unappropriated cel- 

 lulose, stored up in this particular form as the ready pre- 

 pared material for new tissues ; in this respect it performs 

 precisely the same office in the organism of the plant, as fat 

 does in the animal economy. Those differences in the life 

 of herbaceous plants which has occasioned their being de- 

 signated as annuals, biennials, and perennials, results from 

 differences in the quantity of the starch deposited in their 

 roots. The roots of annuals are fibrous, those of biennials 

 and perennials are, on the contrary, thick and tuberous. In 

 the first instance, all the starch is expended in the forma- 

 tion of the flowers and the fruit, the act of reproduction 

 exhausts the vital energies, and the entire plant perishes 

 the first year ; in biennials and perennials, on the contrary, 

 only a portion of the starch formed by the tissues is con- 

 sumed the first year, and the remainder is stored up in the 

 roots, as a reservoir for the growth of the next and suc- 

 ceeding years. In many plants, such for example as San- 

 guinaria Canadensis, the starch accumulated by the leaves 

 through the summer and autumn and deposited in the 

 rhizoma, is consumed by the fiowers in early spring, which 

 appear before the leaves. 



Chlorophyl, next to starch, is the most common of all 

 the cell contents. It is the green matter of plants, and 

 exists in all those parts which are colored green, such as the 

 leaves, sepals, and the bark of the young shoots. It forms 



« See " Precis de Botanique et de Physiologie Vegetale," &o. Paf 

 ^. Biohard, 1852. Premiere partie, pp. 10-11. . 

 10* 



