300 VEGETABLE ORGANOGRAPHY. 



the pollen in the male plants, or the seeds in the females, 

 the whole plant being exhausted dries up and perishes : 

 this forms plants said to be Monocarpient ; that is to 

 say, those which fructify but once at the end of one 

 year (annuals), of two years (biennials), or of several 

 years, as for example in Agave, &c. 



These differences, although constant in each species, 

 since they are determined by causes inherent in its 

 structure, are nevertheless subject to modifications from 

 external circumstances. We can transform an annual 

 plant into a perennial one by preventing it from bearing 

 seeds ; thus, the Mignionette has been changed into an 

 under-shrub which, when once it has a woody stem, 

 flowers each year, without the exhaustion produced by 

 the flowering causing the stem to perish ; thus the dou- 

 ble Nasturtium has become perennial, because its 

 flowers, devoid of the faculty of producing seeds, do not 

 exhaust the stem ; and it is probable that every annual 

 plant, which may be rendered double by culture, will 

 become perennial. 



We may likewise transform, in an analogous manner, 

 a perennial plant into an under-shrub ; this is frequently 

 the case in double pinks. Zizyphus presents a curious 

 phenomenon which renders it, as it were, intermediate 

 between Rhizocarpient and Caulocarpient plants ; we 

 see upon its old trunk kinds of exostoses, from which 

 proceed several simple branches, of which those which 

 bear a great number of flowers disarticulate, and fall after 

 flowering, exactly as the common petioles of pinnate 

 leaves ; whilst those which do not flower, lengthen, 

 remain upon the tree, and form true permanent 

 branches. 



These details tend to prove that the differences in the 

 duration of plants only result very indirectly from their 

 anatomical structure, and serve to explain how, in the 



