ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 481 



Reproductive. 



Gametophytes and Embryogeny in Cunninghamia.*— K. Miyake 

 has studied the development of the gametophytes and the embryogeny 

 in Gunninghamia sinensis, and the results are briefly as follows : The 

 male cones begin to develop in the autumn preceding pollination ; 

 division of the pollen-mother-cell takes place in early spring and is quite 

 typical, the reduced number of chromosomes being twelve. The mature 

 pollen-grain contains a tube-cell and a smaller generative cell, and 

 subsequent to pollination in April, the latter divides into body and stalk- 

 cell. The pollen-cell reaches the female prothallium in June and enters 

 the depression above the archegonium. The enlarged, spherical body- 

 cell passes into the tip of the pollen-tube where it forms two equal 

 sperm-cells, each containing much starch. The female cones likewise 

 develop in the autumn and by the spring a single megaspore mother- 

 cell is formed in each ovule. Division of the megaspore-mother-cell 

 starts about the time of pollination with the synapsis stage when 

 reduction apparently takes place. Of the three potential megaspores 

 the lowest develops into the gametophyte. The female prothallium 

 follows the same course of development as in other Conifers, and when 

 young is surrounded by 2 to 4 layers of tapetal cells ; later on the 

 tapetum is reduced to a single layer, whicli is also more or less dis- 

 organized. The megaspore-membrane is double and well-developed. 

 The archegonial complex of 18 to 16 cells is at the micropylar end of 

 the prothallium, and is surrounded by a layer of sheath-cells : sterile 

 prothallial tissue is found in the centre of the complex. Fertilization 

 occurs early in July. The pro-embryo consists of three tiers of cells, the 

 lowest of which develops into the embryo. Gunninghamia shows thus a 

 close affinity with Taxodium and Gryptomeria, and the three genera are 

 typical Cupressineas, but the sterile prothallial tissue in the archegonial 

 complex seems to show that the first genus is the most primitive. 



Significance of the Periplasmodium.t — E. Hannig continues his 

 work upon this subject, and shows that the tapetum is characteristic and 

 widely distributed. In the Bryophyta the Anthocerotaceas have a 

 primitive tapetum and supporting cells, the Liverworts have a tapetum 

 and elaters, while the Musci have a rudimentary tapetum-spore-sac. 

 All ferns have a true tapetum. The Gymnosperms usually have a tape- 

 turn in both the micro- and megaspore, but that of the latter is often 

 reduced. Among the Angiosperms both the Choripetalas and the 

 Monocotyledons have a typical tapetum in the microspore and a reduced 

 one in the megaspore ; in the Sympetalaj the male tapetum is typical, 

 but the female tapetum has disappeared, being replaced to some extent 

 by the " epithelium " of the integuments. 



The periplasmodium is also a common feature. The tapetal cells 

 remain distinct in the Bryophyta, but the ferns and Equisetaceae have a 

 typical periplasmodium. In the Lycopodineaj the tapetum remains ; in 

 the Psilotacere the periplasmodium is doubtful, and in the Selaginaceae 

 and Isoetaceas absent. The macrospore of the Cycadacea? retains irs 



* Beih. Bot. Centralbl., xxvii. (1911) pp. 1-25 (4 pis. and 2 figs.), 

 t Flora, ii. (1911) pp. 335-82 (3 figs.). 



