68 



THE AMERICAN BOTANIST 



same \YSiy. In practically all cases it is dryness that sets th€ 

 spring by means of which the seeds are discharged. In such 

 pods- there is a layer of elastic tissue that becomes tightly 

 stretched as other parts of the pod dry out. \Mien some weaker 

 part finally gives way, the seeds. are hurled to a considerable 

 distance from the parent plant. A variation of the method is 

 found in the violet and some others in which the initial fracture 

 merely opens the pod and the seeds are eventually discharged 

 by the pressure upon them of the drying and shrinking valves. 

 In the small seed-pods, this bombardment proceeds with little 

 or no noise, but when the species is growing in dense patches 

 the collective popping becomes audible. Thus when the sun 

 shines for a few hours on the silvery phlox (P. argillacca) at 

 just the right time, the miniature cannonade is quite noticeable. 

 Akin to this but still more wonderful is the fact that the open- 

 ing of fern spore-cases may occasionally be heard. If one holds 

 heavily fruited fronds of certain tropical ferns to the ear as they 

 are drying, a continuous crackling sound can be heard due to 

 the opening of countless almost microscopic spore-cases. 



Trees Killed by Mushrooms. — The presence of various 

 mushrooms and allied plants on dead trees and fallen logs is 

 not unusual, but the majority of such species seem incapable 

 of attacking living trees; indeed, some species have entered 

 into partnership with the trees and act somewhat like root hairs 

 in securing food for them. A smaller number, on the other 

 hand, are decidedly harmful. Though unable in the beginning 

 to attack the living parts of the tree, if they once become estab- 

 lished in some injured part, they are able to ultimately extend 

 their depredations to sound tissues. A recent report from the 

 Department of Agriculture accuses the honey colored mush- 

 room (Armillaria incUca) of being one of the worst species in 

 this respect. The underground, vegetative portions of the plant 

 consist of brown or blackish string-like growths that may reach 

 a length of fifteen or twenty feet. These ramify about between 



