HEREDITARY TRANSMISSION AND VARIATION. 83 



know of the reproduction, the perpetuation, and the 

 modifications of the forms of living beings, supposing 

 that we have put the question as to their origination 

 on one side, and have assumed that at present the 

 causes of their origination are beyond us, and that 

 we know nothing about them ? Upon this question 

 the state of our knowledge is extremely different; it 

 is exceedingly large : and, if not complete, our ex- 

 perience is certainly most extensive. It would be im- 

 possible to lay it all before you, and the most I can 

 do, or need do to-night, is to take up the principal 

 points and put them before you with such prominence as 

 may subserve the purposes of our present argument. 



The method of the perpetuation of organic beings is 

 of two kinds, — the asexual and the sexual. In the 

 first the perpetuation takes place from and by a par- 

 ticular act of an individual organism, which sometimes 

 may not be classed as belonging to any sex at all. 

 In the second case, it is in consequence of the mutual 

 action and interaction of certain portions of the or- 

 ganisms of usually two distinct individuals, — the male 

 and the female. The cases of asexual perpetuation 

 are by no means so common as the cases of sexual 

 perpetuation ; and they are by no means so common 

 in the animal as in the vegetable world. You are all 

 probably familiar with the fact, as a matter of ex- 

 perience, that you can propagate plants by means of 

 what are called " cuttings ;" for example, that by 

 taking a cutting from a geranium plant, and rearing 

 it properly, by supplying it with light and warmth 

 and nourishment from the earth, it grows up and 



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