870 EXPERIMENT STATION RECORD. 



It is pointed out, among other things, that the moisture of the soil 

 has a marked influence upon the activity of the microorganisms of the 

 soil which aid in the nutrition of plants, especially the root tubercle 

 bacteria.^ The author's experiments lead to the conclusion that a 

 medium amount of moisture in the soil (50 per cent of that required 

 for comidete saturation) is as a rule more favorable to the development 

 of root tubercles than higher or lower amounts. 



The results of experiments rehiting to the biological effects of dry- 

 ness and humidity on 6 different kinds of soils indicate that different 

 I)lants behave in the same manner as regards resistance to drought, 

 but that the amount of moisture destructive to plants varies with the 

 stage of growth. It is possible, therefore, to trace a curve for each 

 species, showing its water requirements at every period of growth. 



As regards the influence of the moisture of the soil on absorption and 

 transpiration by plants, experiments indicate that (1) the saturation 

 of a soil previously dry produces marked disturbances in the flow of 

 sap; (2) transpiration varies with the water content of the soil, being 

 greater the higher this content; and (3) when the maximum of turges- 

 cence is passed transpiration decreases, there being in fact a maximum 

 of turgescence for each moment of growth at which the functions of 

 nutrition are most active. 



The effect of decapitation on plant organs, B. Rothert {Trans. 

 Assn. Naturalists^ Imp. Univ. Kazan, 26 [1893), iVo. 5, p. 77, Jigs. 2). — 

 The present investigations were conducted by the author to test the 

 statement of Darwin that the cotyledons of Phalaris canariensis, the 

 tops of which had been cut off, did not undergo any heliotropic curving, 

 while those which were uninjured curved rapidly and strongly; from 

 which Darwin concluded that the top of the cotyledon was sensitive to 

 light and that heliotropic curving of the lower part of the cotyledon is 

 caused by irritation transmitted to it from the top, and that the loss of 

 heliotropism was due to removal of the sensitive part of the shoot. 



Following the methods of experiment pursued by Darwin the author 

 conducted a series of experiments with etiolated plants of Phalaris 

 canariensis, in which he proved that decapitation produces but a tem- 

 porary disappearance of heliotropic curving. 



A second series of experiments was conducted with Avena sativa and 

 also P. canariensis, in which the action of the two are so nearly alike 

 that they are described together. From 4 to 7 mm. of the tips were 

 cut from the oats, and from the canary grass the portions removed 

 varied from ^ to 7 mm. The experiments proved that the disappear- 

 ance of heliotropic curving was evidently produced by the wounding 

 of the shoots and is not to be attributed to the removal of the irritat- 

 ing effect when the top is cut. The belief that the disappearance of 

 heliotropic curving might be due to temporary arresting of growth of 

 the rest of the shoots caused the author to conduct a series of experi- 



' Compt, Rend., 116 (1893), No. 24, pp. 1394-1396 (E. S. R., 5, p. 112). 



