300 IN THE GUIANA FOREST. 



ranging facts, which, without some connecting 

 link, would be isolated, confused, and disordered. 



We must premise that, accepting evolution 

 without the slightest hesitation, we are met by the 

 great problem of the origin of variation at the very 

 commencement. The effects of environment when 

 perpetuated become heredity, but this does not 

 explain why two seeds, the offspring of the same 

 parents, and developed under exactly similar cir- 

 cumstances, vary more or less from each other. 

 Natural selection undoubtedly is a factor in the 

 preservation of varieties, but when we come to it 

 for an explanation of how they originate we are 

 baffled. Henslow and Weissman have promul- 

 gated theories which, although not altogether 

 satisfactory, are steps in the right direction, and 

 students will be able to recognise their influence 

 on our own, perhaps, more crude ideas. 



The key to variation is undoubtedly to be found 

 in sexual generation. Every one knows that 

 varieties are more easily perpetuated by cuttings, 

 suckers, and offsets, than from seeds. The sucker 

 is not an individual in the same sense as the 

 seedling, it resembles more those lower animalculae 

 which propagate themselves by division. These 

 have been put down as deathless, for, as long as 

 the species endures so long a part of the original 



