226 THE LIFE OF THE PLANT 



taken root from continuing their existence for an 

 indefinite length of time. The capacity of the plant for 

 reproduction is not limited to such spreading ; it is 

 also manifested in another way. Whole parts of 

 plants, such as stems with leaves, may acquire a special 

 form and then free themselves from the plant that has 

 produced them ; such are, for instance, the little bulbs 

 formed in the angles between the leaves and stems of 

 lilies, and also the tubers that appear on the underground 

 stems of potatoes, in which we can recognise branches 

 only changed in form. We may consider all the plants 

 which spring from these organs as individualised 

 ramifications which have separated from one and the 

 same plant, in consequence of its own rapid spreading. 

 It might seem that these and similar methods of so-called 

 vegetative reproduction are quite sufficient to make the 

 life of a single plant secure for an unlimited length of 

 time ; but matters turn out otherwise. It happens that 

 vegetable life cannot be infinitely prolonged in one 

 direction ; it is bound from time to time to interrupt 

 its course, to ascend again to its source, so that, starting 

 once more from the very beginning, as a single cell, it 

 may retrace the same course in the same order of con- 

 tinuity. In a word, we notice in the life of plants, as 

 well as in the life of animals, a necessary succession 

 of generations, and in each generation an invariable 

 sequence of different stages of development, that we call 

 age. Moreover, it happens that for this periodical 

 renovation not one, but two beings must participate 

 in the formation of a new organism. This is the 

 phenomenon of sexual reproduction. At all levels on 

 the organic ladder, beginning with the weed and ending 

 with man, it presents one and the same phenomenon, 

 which is the blending into one of two beings, two lives, 

 ultimately two cells. 



This inference, that in order to maintain vegetable 

 life, periodical sexual renovation is necessary, is proved 



