ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 349 



leguminous plants. In the main they agree with those of Van Tieghem 

 and Douliot. 



Nitragin in the Nodules of Leguminous Plants. * — Pursuing her 

 investigations on this subject, Miss Maria Dawson has come to the con- 

 clusion that there is probably only one organism capable of producing 

 nodules on leguminous plants, but that in each particular host special 

 physiological conditions exist to which the organism becomes so specially 

 adapted as to make it difficult for successful reaction to take place 

 between plants not nearly allied. Experiments on Pisum, Phaseolus, 

 Desmodium, Bobinia, Acacia, and other genera, show that no definite line 

 of distinction can be drawn between genera in which filaments occur in 

 the nodules and those in which they have not yet been observed. 

 Peculiar anatomical characters were observed in certain genera, e. g. a 

 definite crystal layer in some cases ; apple-green nucleus-like bodies in 

 Desmodium and Bobinia, organisms of an unusually large size in Desmo- 

 dium, Coronilla, Psoralea, and others. 



j3. Physiology. 

 (1) Reproduction and Embryology. 



Double Impregnation in Tulipa.t — M. L. Guignard has extended 

 his observations on the process of double impregnation or " pseudo- 

 fecundation " to other genera besides Fritillaria and Lilium. In Endy- 

 mion (Scilla) nutans nothing of the kind could be detected. The two 

 polar nuclei, whose union gives rise to the secondary nucleus of the 

 embryo-sac, approach one another long before the entrance of the 

 pollen-tube into the ovule, remaining, however, perfectly distinct from 

 one another. Endymion presents in this respect a phenomenon inter- 

 mediate between that of Lilium and that of Fritillaria. 



In Tulipa there is a remarkable difference between the processes in 

 the cultivated varieties of T. Gesneriana and those in the wild species 

 T. Celsiana and T. sylvestris. In the former there is no important 

 departure from the ordinary structure of the embryo-sac. In the last- 

 named two species the embryo-sac is ovoid, and contains at its base a 

 large vacuole. Eight nuclei are formed in the usual way by three 

 successive bipartitions of the primary nucleus; but, instead of these 

 being grouped into two tetrads, they all remain, at nearly equal dis- 

 tances from one another, in the protoplasm above the vacuole. Two of 

 the eight are smaller, and evidently represent the synergids ; of the 

 remaining six, one is situated on a lower level than the others, and has 

 a delicate chromatic framework and numerous nucleoles. But the nucleus 

 which corresponds to the oosphere does not differ in any conspicuous 

 respect from the other nuclei. When the pollen-tube enters the embryo- 

 sac, one of its " antherozoids " fuses with the nucleus which represents 

 the oosphere, the other with the nucleus which represents the superior 

 polar nucleus ; the two combined then reuniting with the basal nucleus. 

 The coalition of the polar nuclei presents essentially the same characters. 

 The remaining nuclei are gradually resorbed. 



M. Guignard records that he has observed a process of double fecunda- 

 tion also in the Kanunculacese. 



* Proc. Koy. Soc, lxvi. (1900) pp. 63-5. Cf. this Journal, 1899, p. 296. 

 t Comptfs'Rendus, exxx. (1900) pp. 681-5. Cf. this Journal, 1899, p. 409. 



