TUMOURS OF PLANTS. 533 



in consequence of the puncture of an insect, the tuberous 

 swellings which mark the spots on a tree where a bough 

 has been cut off, and the wall-like elevation which forms 

 around the border of the wounded surface produced by 

 cutting down a tree, and which ultimately covers in the 

 surface all of them depend upon a proliferation of cells 

 just as abundant and often just as rapid as that which 

 we perceive in a tumour of a proliferating part of the 

 human body. The pathological irritation acts in both 

 cases precisely in the same manner ; the processes in 

 plants conform entirely to the same type, and just as lit- 

 tle as the tree produces on its bark or leaves cells of a 

 kind, which it could not bring forth at other times, just 

 as little does the animal body do this. 



But if you consider the history of a vegetable tumour, 

 you will see there also that it is above all the diseased 

 spots which become unusually rich in specific constitu- 

 ents, and absorb and store up the peculiar substances 

 which the tree produces, in more than average quantity. 

 The vegetable cells which form on an oak-leaf round the 

 puncture made by an insect contains much more tannic 

 acid than any other part of the tree. The tumour-cells 

 which form with such exuberance in a pine at the spot 

 where an insect has buried itself in the young trunk, are 

 stuffed completely full of resin. The peculiar formative 

 energy which is developed at these spots, occasions also 

 an unusually abundant accumulation of juices. There 

 is no need of any nerves or vessels to instigate the cells 

 to an increased absorption of matter. It is by their own 

 action by means of the attraction which they exercise 

 upon the neighboring fluids that they draw in the most 

 serviceable materials. The great importance, which a 

 knowledge of botany possesses for the pathologist also, lies 

 in this that it enables him to discover in all these pro- 

 cesses the existence of an inward correspondence in the 



