ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 195 



Function of the Starch-Sheath.* — F. Tondera concludes from his 

 investigations of internodes of various members of the order Cucurbi- 

 taceag that the function of the starch-sheath is not statolithic. The 

 position of the starch-grains on the cell-wall is not a constant one, nor 

 is their distribution in the layer and on the cell-wall such as we should 

 expect on Haberlandt's Statolithic theory of Geotropism. Nor is the 

 starch-sheath to be regarded as the path for plastic material, but as a 

 store-house for nutrient matter required in the immediate neighbour- 

 hood ; observation shows that the starch-grains are used up in the 

 thickening of the cellulose walls of the sclerenchymatous ring. No- 

 starch-sheath was found in the following three species, Bryonia dioica, 

 Luffa acutangula, and Trichosanthes colubrina. This is explained by 

 the large size of the vascular bundles, the sieve-tube area of which, 

 comes to lie close to the thickening ring, which is thus fed directly from 

 the bundle, and obviates the;necessity of a temporary storage of starch 

 in a starch-sheath. 



Influence of the Nature of the Soil on the Organic Composition of 

 Plants.j — A. Hebert and E. Charabot find, as the result of experiments 

 with peppermint, that in mature plants the proportions of ash, of organic 

 substance and of the elements which compose the latter — carbon, 

 hydrogen, nitrogen and oxygen — show very little variation when different 

 salts are added to the soil. This fact is very evident when the per- 

 centage composition of dried plants is examined. Thus in the aerial 

 organs the ash varies from 8 - 6 to 11, organic matter from 81 to 91 '4 • 

 while of the component elements of the latter carbon varies from 44 • 6 to 

 46 • 5, hydrogen from 5 ' 6 to 5*8, nitrogen from 1 • 2 to 1 • 6, and oxygen- 

 from 86 to 40. Calculated in numbers of atoms, the variation is — 



C H N C H N 

 4-1 6-1 "09 2-5 to 4 6'6 "08 S3 



for aerial organs, and 



C H N C H NO 

 8-7 G -05 2*8 to 4 6*6 '08 3 



for roots. 



Irritability. 



Relation between Light Intensity and Energy of Assimilation 

 in Plants belonging to different Biologic Types.! — Fr. Weis has ex- 

 perimented with plants of Marchantia polymorpha, Polypodium vulgare y . 

 and Oenothera biennis, exposing them to light of different degrees of 

 intensity under conditions in which the amount of oxygen evolved and 

 carbon dioxide absorbed could be determined. In experiments in direct 

 sunlight the tubes containing the plants were placed under bell-jars 

 with double walls, between which passed a continuous current of cold 

 water to absorb the heat rays of the sunlight. The plants were exposed 

 to direct sunlight and light ^ and ^ the intensity of direct sunlight. 

 The intensity was estimated by the time taken by photographic paper 



* Bull. Internat. Acad. Sci. Cracov. CI. Sci. Math, et Nat., 1903, pp. 512-6 (1 pi.), 

 t Comptes Eendus, cxxxvii. (190:!) pp. 799-801. 

 % Tom. cit., pp. 801-4. 



