CHAP. V. FUNCTION OF REPRODUCTION. 253 



in Germany about the middle of October ; a retardation 

 in this case which is less than in the former. 



When a perennial has once begun to flower, it is 

 subject to periodic returns of this function. The period 

 of the year in which the flower expands, is regulated in 

 all cases by the peculiar character of each individual, 

 and it is very nearly the same for all plants of the same 

 species. There are, however, remarkable exceptions to 

 the laws by which the periods of flowering in different 

 species are regulated. Advantage is taken of this cir- 

 cumstance ; and by propagating from such individuals 

 as are both the earliest and latest in producing their 

 seeds, peculiar " races " are gradually established, which 

 secure to the cultivator a longer succession of a given 

 crop than he could otherwise have obtained. De Can- 

 dolle mentions an instance of a horse-chestnut at 

 Geneva, which always flowers a whole, month before 

 the rest in its neighbourhood, without any apparent 

 cause for such precocity. These anomalies indicate 

 some peculiarity of constitution, or " idiosyncrasy," in 

 the separate individuals ; but they determine nothing 

 against the existence of a general law, by which each 

 species is supposed to be regulated in producing its 

 flowers at a certain period of the year. A very abun- 

 dant crop of fruit generally absorbs so much of the 

 nutriment prepared in the stem, as to diminish, and 

 often entirely to prevent the formation of flowers 

 in the following season ; and hence, some trees in 

 orchards bear abundantly only on alternate years. As 

 double flowers produce no fruit, their stems are 

 not so thoroughly exhausted ; and perennials of this 

 description generally flower earlier in the season than 

 single flowers of the same species. By far the greater 

 number of plants flower in the spring, and several 

 do so even before they expand their leaves. In these 

 cases, the nutriment which has been prepared for the 

 development of the flower, must have been wholly 

 provided by the leaves of the preceding season, and 

 have been magazined through the winter in the stem. 



