RELATIVES OF THE FERNS 57 



It may be explained that the wall of the 

 Equisetum spore is three-layered, and outside 

 of these is a layer which is formed into four 

 long arms. Thus, when magnified, the body 

 resembles a ball with four long clubbed 

 threads attached to it. These are seen to be 

 constantly on the move ; even as one watches 

 them through the microscope they are twist- 

 ing about in a most singular manner, at 

 times being fully extended, and at others 

 wound closely round the spore itself. The 

 constant movement is due to the sensitiveness 

 of the threads to changes in the degrees of 

 moisture in the atmosphere. Blow lightly on 

 the slide, and at once aU the spores change 

 their position in response to the damp breath. 

 One purpose served by these active threads 

 seems to lie in the linking up of a number of 

 grains, so that the spores may float about arm 

 in arm, so to speak. They are so light that 

 even an aggregation of them can be wafted by 

 the very Ughtest breeze. The writer has made 

 several attempts to secure photo-micrographs 

 of Equisetum spores, but on account of the 

 continuous movement this has been quite 

 impossible. 



