MOVEMENTS OF IRRITATION". 433 



plasm. If, viz., we expose our preparations to direct sunlight for a 

 considerable time (in my experiments with Funaria leaves for f 

 hour) the chlorophyll grains will pass from the outer and inner 

 Avails of the cells to the side walls, and dispose themselves in the 

 profile position. The grouping of the chlorophyll grains in the 

 surface position on the outer and inner cell-walls is, however, re- 

 sumed if A the preparations are exposed for some time to diffuse 

 daylight. There is no doubt that these changes in position of the 

 chlorophyll bodies are of biological importance to the plants. In 

 diffuse light the green constituents of the cells take up a position 

 which will enable them to make use of the rays of light for the 

 purpose of assimilation in a very thorough manner, while they 

 will be protected from the destructive influence of too intense 

 light and too great warmth by the arrangement on the side walls 

 of the cells. 1 



The movements of the chlorophyll bodies caused by the 

 stimulus of light are only exhibited when the cells are exposed to- 

 normal conditions of life. Too great reduction of temperature, 

 insufficient moisture, and want of Oxygen prevent them, as can 

 easily be proved by suitable experiments. 



See Sta'hl, Botan. Zeitung, 1880, p. 321. 



171. The Movements of the Plasmodia of Aethalium septicum. 



The plasmodia of the Myxomycetes are capable .of peculiar 

 movements ; they can creep from one place to another, their out- 

 lines constantly changing in the process. These movements are 

 very largely influenced by external conditions, a fact which is of 

 the utmost biological importance to the plasmodia. Aethalium 

 septicum is chiefly found on tan. The yellow plasmodia are to 

 be found in spring (e.g. in May, during which month I made 

 numerous experiments on the plasmodia) on the older masses of 

 tan. There further appear, however, on the tan, at this time, as 

 also in winter, Aethalium sclerotia, in the form of small knob-like 

 yellow masses, about 2 mm. in length, from which we can readily 

 obtain plasmodia. It must here be emphatically remarked, that 

 the plasmodia are very delicate structures, easily killed, and 

 sensitive to contact with the hand. Consequently the masses of 

 tan, with the plasmodia traversing them, must be handled care- 



P.P. F F 



