ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 331 



remainder, 381, or 9fi'S p.c., responded better for the deviation of 

 90° ; 11, or 3*2 p.c, for the deviation of 135°. In the second method, 

 orthotropic plant members are exposed to the one-sided action of gravi- 

 tation by being placed out of their normal position ; but before a 

 geotropic curve has time to appear, the plant is put upon the klinostat, 

 and so revolved that the further curving effect of gravitation is neu- 

 tralised during the revolution. Thus, any geotropic influence induced 

 in the plant before it was placed on the klinostat, has opportunity to. 

 show itself. If the gravitation effect on plants differs according to the 

 deviation of the plant from its normal position, we may expect the size 

 of the after-effect angle attained on the klinostat to be greatest when 

 the previous exposure of the plant was made at the angle of optimum 

 stimulation. The results obtained were less satisfactory than with the 

 previous method, but when any difference in after-effects could be 

 observed, it was in agreement with the results of the alternation experi- 

 ments. Hence there is strong evidence that stems respond better to the 

 gravity stimulus when their angle of deviation from the normal position 

 is one of 90° than when it is one of 135° ; and since the question seems 

 to have been narrowed to these two angles by previous workers, it may 

 be claimed that the angle of deviation from the vertical at which stems, 

 show the strongest geotropic response is one of 90°. 



Distribution of Statoliths in Roots.* — G. Tischler has studied the- 

 distribution of starch grains in ageotropic, or slightly geotropic roots. 

 He finds that in adventitious roots which are constantly ageotropic, 

 starch-grains are either not present in the root-cap, or, if present, are 

 irregularly distributed ; and the same holds for temporarily ageotropic- 

 roots. When roots become slightly geotropic, the starch-grains appear 

 and function as statoliths. The author suggests that in certain aerial 

 roots of orchids, which are slightly geotropic but do not contain starch- 

 grains, the chloroplasts of the root-cap act as statoliths. 



The Effect of Low Temperature on Zoospores of Algae.j — E. C. 

 Teodoresco describes four experiments made by him on the zoospores of 

 Dunaliella in very low temperature. In one case zoospores of the 

 alga were placed in very concentrated salt water, and exposed for three- 

 months to a temperature which at times went as low as 20° below 

 zero. The zoospores remained alive and in good condition. They did 

 not encyst, nor pass into the Protococcoid state. In another experiment, 

 zoospores of the same alga were placed in a tube of salt water concen- 

 trated to 38° Baume, and the tube was sunk for six minutes into a 

 mixture of equal parts of snow and alcohol. The temperature varied 

 between — 30° and —29°, but the zoospores remained alive and swam 

 about with ease. The same tube was then placed in the freezing mixture 

 for thirty minutes, during which time the temperature varied between 

 — 30° and — 26 3 . The salt formed a transparent layer at the bottom 

 of the tube, while the water above it was transformed into a sort of 

 opaque, whitish, soft snow. After 30 minutes the tube was removed 

 to a temperature of —2°, where the snow melted. The zoospores were 

 found to be for the most part alive and mobile ; and when placed in a 



* Flora, xciv. (1905) pp. 1-68. t Comptea Rendus, cxl. (1905) pp. 522-4. 



