ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 81 



tubes filled with contents. Similar tubes are also found, in great 

 abundance, in the absorbing roots. 



j8. Physiology. 

 (1) Reproduction and Embryology. 



Embryology of Corylus.* — Prof. S. Nawaschin has made a further 

 investigation of the processes connected with the formation of the embryo 

 and the act of impregnation in the hazel, and discusses the analogies 

 with the corresponding processes in the Betulaceae and the Casuarineas. 

 While these processes correspond, in the main features, with those in 

 the birch, they differ in this respect, that in the hazel there is not a 

 single sporogenous cell (the mother-cell of the embryo-sac), but a 

 sporogenous tissue composed of a varying number of cells, up to 12, 

 from which are derived, by further division, a number of megaspores, 

 which may amount to 20 or more, though sometimes there is only a 

 single one. The sister-cells of the megaspores become atrophied. The 

 alder presents, in some respects, an intermediate condition between the 

 birch and the hazel ; while the processes in the hazel lead on to those 

 in the Casuarineaa. The further development of the only megaspore 

 which matures presents no special features. 



Before impregnation there is, in the hazel, no typical egg-apparatus. 

 The ..position of the antipodals corresponds more nearly to that of an 

 ordinary egg-apparatus, viz. near the apex of the embryo-sac ; the anti- 

 podals finally clothe themselves with cellulose-membranes. In the 

 mature embryo-sac the egg-apparatus is replaced by a mass of protoplasm 

 with free-lying nuclei. 



Impregnation by the pollen-tube takes place chalazogamically ; 

 pollen-tubes are constantly to be met with within the nucleus in the 

 neighbourhood of the funicle. The actual contact of the apex of the 

 pollen-tube with the egg-apparatus is exceedingly difficult to follow. 



(2) Nutrition and Growth (including 1 Germination, 

 and Movements of Fluids). 



Symbiosis and Saprophytism.f — Prof. D. T. MacDougal limits the 

 term saprophyte (or holosaprophyte) to those species which derive their 

 food-supply from organic products directly, without the intervention of 

 the activity of chlorophyll and unaided by other organisms. If the 

 term be thus limited, holosaprophytes include numerous fungi and 

 bacteria, but as far as we know at present, only one seed-forming species,. 

 Wullschlaegelia aphylla. All species furnished with mycorhiza or 

 tubercles, or which enter into direct mechanical or nutritive associations,, 

 must be classed as symbionts or " symbiotic saprophytes." 



The degenerations of the true saprophytes are generally parallel to 

 those of mycorhizal forms. All endotropic mycorhizas do not conform 

 to a single physiological type. The theory of Janse, $ that endotropic 

 fungi are negatively chemotropic to oxygen, and bear the same relation 

 to the higher plants as the organism of the leguminous tubercle, is not 



* Bull. Acad. Imp. Sci. St. Pe'tersbourg, x. (1899) pp. 375-91 (2 pis.) (German). 

 Cf. this Journal, 1895, p. 654. 



t Bull. Torrev Bot. Club, xxvi. (1899) pp. 511-30 (3 pis. and 1 fie.). Cf. this 

 Journal, 1899, p. 505. J Cf. this Journal, 1897, p. 318." 



Feb. 21st, 1900 G 



