258 THE LIFE OF THE PLANT 



It is impossible to distinguish this movement from 

 that of the infusoria, and it is so contradictory to the 

 current ideas as to the non-mo tility of the plant, that 

 the first observers of similar phenomena refused to 

 believe the evidence of their own eyes ; they would 

 not believe that these bodies were of a vegetable nature. 

 They attributed this movement to animals developed 

 inside the plant. These motile cells after a time come 

 to rest, germinate, and give rise to a new organism — 

 they are therefore spores. In order to mark their 

 resemblance to animals, they are called zoospores, i.e. 

 animal-spores, or rather motile, wandering spores. 

 Let us study one more zoospore, but from another class 

 of plants, the water-weeds. There appears on sub- 

 merged objects in ponds, streams, and ditches, occa- 

 sionally also upon the surface of very damp soils, a 

 bright green weed consisting of a single much-branched 

 tubular cell. If we leave such a weed in summer in a 

 glass of water, we shall notice every morning a curious 

 phenomenon : a narrow, bright green line will appear 

 on the surface of the water, at the side of the glass which 

 faces the light. If we move the glass so as to turn the 

 green edge away from the light, we shall observe that 

 the green line will disappear, to reappear again at the 

 side towards the light. We can repeat this experi- 

 ment many times and always obtain the same result. 

 This green matter is evidently capable of movement, 

 and moves always towards the light. Let us investi- 

 gate the constituents of this green matter and its origin. 

 We place it in a drop of water under the microscope 

 and notice that it swarms with green cells swimming 

 to and fro (fig. 75, I., on the top). The cells have no 

 walls ; they consist of a lump of protoplasm spangled 

 with shimmering cilia all over the surface. Let us now 

 turn our attention to the weed itself and see what is 

 its relation to these motile green cells. We shall 

 notice pin-head swellings at the end of its green tubes, 



