ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 91 



while ill the Sttiticeie the nuclei divide as usual and form an eight- 

 nuclear embryo-sac, the closely related group of the Plumbaginese 

 liehave in a totally different manner. The species upon which most of 

 the observations were carried out was Plumhayella micrantha, but three 

 species of PJuwJmijo and Geratnstigma phimbaginoides all exhibit the 

 same peculiarity in their embryogeny. After the two meiotic divisions 

 no further division takes place, l)nt the four macrospore nuclei constitute 

 the embryo-sac. The uppermost nucleus becomes the nucleus of the 

 egg-cell, the lowest the antipodal nucleus, and the remaining two the 

 polar nuclei. The two latter fuse very early, some time before fertiliza- 

 tion. No synergidse are ever present. It is probable that a secondary 

 embryo-sac nucleus is formed, although it has not yet been observed. 

 The antipodal nucleus and cell soon disappear. At the time of fertiliza- 

 tion the pear-shaped egg-cell fills the upper part of the embryo-sac ; its 

 plasma is mainly confined to the broad lower end, while in the upper 

 part is a large vacuole. The endosperm-nucleus lies close against the 

 egg-cell. The actual process of fertilization has not yet been seen. 

 Thus the Plumbagineas appear to represent the utmost limit, at present 

 observed, of the tendency in the higher plants to reduce the gameto- 

 phyte to an organ of the sporophyte generation. The author likewise 

 points out the surprising similarity in the results of the reduction- 

 division in this group, and in animals, and shows tliat it is conceivable 

 that cases mav occur where the embrvo-sac and the egg-cell are 

 identical. 



Cratsego-Mespilus Graft-hybrids.* — J. Meyer has studied the two 

 " graft hybrids " described by Bronvaux, which originated from the 

 callus formed at the junction between a Cratsegus monogyna stock and 

 a scion of MesplliiS gennanica. Few distinguishing features occur 

 between the tissues of Cratsegus and Mespilas, but the chromosomes of 

 M. germanica are longer and thinner than that of G. monogyna. The 

 capacity to produce anthocyan is present in the epidermis of the fruits 

 of Cratsegus, but lacking in fruits of Mespihi>i, while, on the other hand, 

 3Iespilus flowers turn reddish in ageing, while those of Crataegus remain 

 white. There are also differences in the shape of the epidermal cells 

 and the cuticle. The author supports the view of Baur, that these two 

 '• graft-hybrids " consist of a core of Cratsegus tissue overlaid by a 

 mantle of Mespilus. In one of the two the mantle is a single epidermal 

 layer, while in the other the first sub-epidermal layer is a bit of Mespilus 

 tissue. This sub-epidermal layer may divide periclinally to form a 

 number of cell-layers, in one case as many as eiglit. As lateral 

 branches originate from periclinal divisions in the second sub-epidermal 

 layer. Meyer maintains that no graft-hybrid could maintain itself as 

 such in which the mantle should consist of more than two layers. 



* Zeitschr. Ind. Abstamm. Vererb., xiii. (1915) pp. 193-233. See also G. H,. 

 Shull, in Bot. Gaz., Ix. pp. 323-4. 



