ZOOLOGY AND BOTANY, MICROSCOPY, ETC, 1U29 



out of the anthers by the hairy style at a period anterior to the 

 maturation of the stigmas ; before the occurrence of which the 

 pollen has disappeared from the style. In this manner cross-fertiliza- 

 tion is rendered certain. The pollen developes normally. The 

 stigmas are held together until mature by interlocking papillae. 

 The hairs on the style become partially introverted, and thus free the 

 pollen. 



The pollen-grain contains two nuclei, tbe larger of which, the 

 vegetative nucleus, becomes disorganized shortly after entering the 

 pollen-tube, while the smaller spindle-shaped generative nucleus per- 

 sists. The embryo-sac is cylindrical, with a gradual enlargement 

 near the micropylar end, where is located the egg-apparatus, and an 

 abrupt enlargement at the chalazal end, in which lie the antipodal 

 cells. The embryo-sac has usually two nuclei. The pollen-tubes 

 enter the style between the bases of the iiapillte of the stigma, pass 

 down in the strands of the conducting tissue, and not through the 

 central canal around which this tissue is arranged. 



Influence of Want of Moisture on the Growth of the Chinese 

 Yam.*^M. P. Ducliartre has made a series of experiments on the 

 effects of diflerent degrees of moisture on the growth and structure of 

 Dioscorea Batatas. The results are given in considerable detail, with 

 the general conclusion that, at all events as regards this particular 

 species, water, as an alimentary substance, promotes essentially tlie 

 formation of parenchyma, without, in an appreciable degree, affecting 

 the strengthening anatomical elements. 



Mechanical Injury to Trees by Cold-t — Prof. T. J. Burrill 

 deals with two mechanical effects of cold up(m trees: tlie radial 

 splitting of wood and bark, and the separation of bark or wood layers 

 in a concentric way. 



The first is explained by water freezing in plates parallel to the 

 surface of an organ, and then, additions being made to the base, 

 crystals perpendicular to the surface will be formed. Thus the wood 

 contracting, and the ice expanding tangentially and longitudinally 

 (chiefly the former), radial bursting is the result. The south side of 

 a tree is the weakest, as more water exists there, and ice is first 

 formed. Direct observation shows that the specific gravity of sap is 

 greater on the north side of a tree. 



Concentric splitting is explained by minute ice-crystals forming 

 with their axes perpendicular to the wood-cylinder, thus causing 

 radial tension. Want of rijieness of tissue, in the sense of the 

 relation of water to other constituents, is the chief predisposing 

 cause. 



Essential Food of Plants.^— Wliilst no doul)t exists as to the 

 essential character of the elements of carbon, hydrogen, oxygen, and 

 nitrogen as constituents of the food of plants, the evidence in support 



• Bull. Hop. IJot. Fn.ncft, vii. (18S5) pp. UiC-Gl. 

 t r.ot. (i:>7A-tUt, X. (IHKf); ].p 8:54-.'). 



♦ Nature, xxxii. (iHhiy) p. .0:^8. (I'aj cr icad Ijcforo the FWliHh Awsofiiition, 

 Section h.) 



H<r. 2.— Vol.. V. [i X 



