364 



Mr. F. Darwin. 



[Mar. 6, 



starch if kept for periods varying from 6 — 26 hours at a high tempera- 

 ture, e.g., 33 — 38. Such seedlings show a marked loss of geotropic 

 movement. 



Exp. 201, March 3, 1902. 



Eight specimens of Sorghum, vulgar e were kept for 2 If hours at 

 37°, and others at 16 '5° — 19° C. They were then allowed to curve 

 geotropically for 20h. 20m. when the " cool " lot showed an average 

 curvature of 49 - 8°, while the " hot " specimens gave an average of 9°. 



Exp. 204, March 4, 1902. 



Twelve specimens of Sorghum vulgare in two equal lots for 21h. 5m. at 

 37° and at about 18°. Microscopic examination at the close of the 

 experiment showed considerable irregularity in the disappearance of 

 starch, and the following table shows that the degree of geotropic 

 curvature is more or less parallel to the amount of starch remaining. 



1. 1 Starch in small quantities 72° (geotropic curve). 



2. J „ „ 70° 



3. Less starch than 1 and 2 33" 



4. Starch almost disappeared 20° 



5. \ „ „ 28° 



6. J „ „ ....... 11° 



At first I was inclined to see in facts like these a striking con- 

 firmation of the statolith-theory, but experiments of the type of the 

 two following prove conclusively that such an opinion is not justifiable. 



Exp. 215, March 13, 1902. 



Sorghum nigrum nearly de-starched by 6 hours at 40° C. On the 

 following day exposed to incandescent gas for 4 hours. 



Eesult — Cool, 40° '2 (average curvature to light). 

 Hot, 10*-6 



Exp. 223, March 26, 1902. 



Sorghum nigrum nearly de-starched by 5h. 35m. at 33° — 34° C. 



Part of them were then placed horizontally in the dark for 4 \ hours, 



the remainder being vertical and exposed to incandescent gaslight 

 for the same period. 



Eesult. — Geotrojrism (average) Cool 47° Hot 7 C '2 



Heliotropism ,, „ 21° ,, 7°'7 



These and other similar experiments showed us that we had no right 

 to conclude that the loss of geotropic capacity depended on the 

 absence of the special mechanism (statoliths), but rather that the loss 

 of the starch may perhaps be no more than a symptom of exhaustion 

 which shows itself both geo- and heliotropically. 



Nemec has shown that in decapitated roots, i.e., roots from which 



