BOTANICAL SUBJECTS. 59 



v.— SOME FACTORS OF MODIFICATION IN 



PLANTS. 



Conjugation. 



The coming together of the sexes appears to have but one 

 universal object, both in animals and plants. This object is the 

 conjunction of two differentiated cells — a sperm cell "with a germ 

 cell. This union is now acknowledged to be the mainspring of 

 modification in living things, although verv probably not the only 

 one. The longer the series of ancestors which is at the back of 

 each of the cells that conjugate, the more variation is likely to 

 ensue. 



Therefore, multiplication by sexual -(processes, in contradis- 

 tinction to that by axesual ^^rocesses — that is, multiplication by 

 fertilized seed, as distinguished from multiplication by ordinary 

 bud — would appear the main factor of modification. 



Surroundings. 



Then there is climate, with its heat or cold, di-yness or 

 moisture, &c. ; soil, with its looseness or hardness, its rockiness, 

 its vegetable mould, its dampness or total want of moisture, and its 

 variety of mineral ingredients. 



I am aware that many do not admit that surroundings of this 

 kind can so influence an organism as to enable it to transmit any 

 acquired modifications to its offspring. But it is not believable 

 that, when the organism is unicellular it is modified by its sur- 

 roundings, as Weismann says, and when these unicellular bodies 

 aggregate, those that become reproductive cells are 710 longer 

 modifiable, through surroundings, either directly, or by way of 

 their nurses, which are now the sofnatic cells.* 



I know it is difficult to prove that any modification has 

 occurred through the transmission of any acquired character due 



' ' Or body cells, as distinguished from the reproductive cells. 



