30 COJIPOUND OEGANS OF PLANTS. 



earth, he was visited by a Catholic priest, who accused him of 

 Atheism. The persecuted and venerable sage met the accusa- 

 tion by the following beautiful and sublime, though simple and 

 affecting appeal. He took from the floor of the dungeon on 

 which he was lying a wheaten straw, and having explained the 

 mechanical and scientific principles shown in the structure of 

 the stem, told the priest that this was evidence to his mind of 

 the existence of a God. " If," said he, " this wheaten straw, 

 which supports an ear heavier than its whole stock, were made 

 of the same quantity of matter disposed in a solid form, it 

 would make but a poor thin and wiry stem, which would be 

 snapped with the slightest breeze; its tubular form gives it the 

 necessary degree of strength, and preserves it from destruc" 

 tion." 



Not only the strength hut the duration of stems depends on' the 

 degree of their development. A plant is considered to be a 

 herb if its stem invariably dies down to the ground each year. 

 Some herbs are only annuals arriving at their full development 

 and the term of their existence in one year, the act of repro- 

 duction exhausting their vital energies. In biennial herbs the 

 whole of the nutriment assimilated by the vegetative organs 

 the first year is consumed by the act of reproduction in the 

 second, and the plant necessafily perishes. In herbaceous 

 perennials the upper part of the plant only dies, life retrea ts 

 into the rhizoma, and with the return of light and heat to th e 

 earth in Spring, the plant again makes its appearance above 

 the ground, and developes into its wonted figure and hues. 



The same species may become an annual, biennial, or even a 

 perennial, according to the treatment which it receives, and 

 the circumstances in which it is placed. If an annual plant be 

 deprived of its flowers and preserved from the inclemency of 



