Polytechnic Association Proceedings. 939 



meters (nearly twenty inches) was not influenced by frost. After 

 these experiments, Mr. Reiset had told agriculturists that they were 

 utterly mistaken, if they trusted to frost for the preservation of 

 their crops from insects, and that they must exert themselves if 

 they wished to escape the impending scourge. Knowing that last 

 autumn the white worm was still near the surface, he caused a field 

 to be slightly plowed and harrowed; and two persons following 

 the harrows gathered three hundred and forty-four kilogrammes 

 of worms, at a cost of twelve francs per hectare (two and a half 

 acres). This field produced an excellent crop, while that next to 

 it, from which no worms were gathered, produced nothing. 



INFLUENCE OF LIGHT ON MICK0SCX3PICAL ORGANISMS. 



Prof. F. Cohn has made interesting experiments with the mouth, 

 less genera of infusoria, which are provided with cilia, and those 

 genera of microscopical plants which are possessed of an inde- 

 pendent power of migration. He finds they all move in a definite 

 direction, and that the immediate cause of movement is light. In 

 colorless organisms light has no influence, and they appear to move 

 in every possible direction. Experiments with euglena gave the 

 following results: If a drop of water, equally filled with these 

 green organisms, be placed upon a glass slide, it will be seen, 

 before many minutes, that they will betake themselves to that por- 

 tion of the drop which is turned toward the window, or even 

 toward that part of the sky which is most lightened. They crowd 

 around this side, which we may call the window side, and give the 

 drop a green edge, while the rest of the drop is quite colorless, 

 and free from euglenae; and indeed they place themselves together, 

 so that their heads lie parallel one to another, toward the light, 

 and their bodies are directed perpendicularly to the edge of the 

 window. They cannot remove themselves from this position, but 

 gradually dry up as the water on this edge becomes evaporated. 

 Conversely, if the drop be moved, so that that which was formerly 

 the window side is now turned away from the window and directed 

 toward the room, by which the former room-side forms the win- 

 dow-side, an instantaneous movement in the whole of the organism 

 will be seen, for the purpose of turning themselves round. The 

 foremost soon turn round and swim toward the window edore, and 

 the back ones follow one after the other. In the course of two or 

 three minutes they have all taken their new positions. This experi- 

 ment when repeated gives the same result, whether the drop lies 



