214 CHLOROPLASTS. [CH. VIII 



dark room of which the floor is occasionally watered. 

 According to the same authority the air should be in such 

 a condition that the difference between the wet- and dry- 

 bulb thermometers is 1-5°— 2-0° R. (2°— 2-5° C). We 

 find it a good plan occasionally to squirt with water the 

 lower surface of the sieve. 



(248) Movement of chloroplasts. 



We find that the leaves of Oxalis acetosella^ give good 

 results. Ten or twelve leaves are taken from a plant, and 

 after the stalks have been cut short off beneath the 

 pulvini they are placed floating in water. Half of the 

 number in one dish are exposed to bright sunshine, the 

 rest remain in dull diffused light. After two hours they 

 may be examined by preparing surface sections of the 

 spongy parenchyma. In the sunned leaves the chloroplasts 

 are in the " profile position," that is, they lie against the 

 side walls of the stellate parenchyma cells, and may even 

 be crowded into the corners. In the shaded leaves they 

 are spread out and dotted over the surfaces which are 

 parallel to the plane of the leaf The leaves may be pre- 

 served in alcohol for future examination. 



(249) Ghemotaxis: antliey^ozoids. 



The following instructions are taken from Pfefifer's 

 paper in his Untersuchungen\ The prothalli which yield 

 the antherozoids for Pfeffer's experiments were chiefly 



1 This plant is recommended by Stahl, Botanische Zeitung, 1880, 

 Stahl's figure of Oxalis is copied in Frank's Lehrhiich, p. 289. 



2 Untersuchungen aus dem hotanischen Institut zu Tilhingen, i. 1881— 

 1885, p. 363. 



