ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 439 



from the centre towards the outside. When the thickening and stretch- 

 ing reach the outermost row of cells, the growth in thickness of the 

 stem comes to an end. 



Anatomy of the Madagascan Raphia.* — R. Claverie has examined 

 various specimens of Raphia, and considers that the anatomic characters 

 upon which Sadebeck bases his two species are insufficient ; the anatomy 

 of the specimens now examined would show four species, but the author 

 believes that it would be better to consider the number of fibres in each 

 bundle, the diameter of each fibre, and the thickness of the membrane, 

 rather than the points considered by Sadebeck in making his classifica- 

 tion. The possibility of the existence of several species is confirmed by 

 the variety of the fruits supplied from the same sources, and the author 

 believes that the preference given to Raphia grown upon the west coast 

 is not justified, since the characters of " Raphia clair " are often found 

 in specimens grown on the east coast, and vice- versa. 



Reproductive. 



Development of Microsporangium in Cycads.f — F. G. Smith has 

 investigated Zamia jioriclana and other Cycads with special reference to 

 the development of the microsporangium. The sympodial stem of 

 Zamia has a vegetative point at the base of each strobilus, from which the 

 staminate strobili successively develop, each with a circle of leaves, and 

 all inclosed in the scale-leaves of the first strobilus. The staminate 

 sporophylls arise in acropetal succession, at first from one, and later on 

 from several liypodermal cells. The microsporangia are grouped in two 

 sori, but their position on the sporophyll varies. The archesporium is a 

 single hypodermal cell, the outer divisions of which give rise to the wall, 

 and the inner ones to the sporogenous tissue. The wall of the sporan- 

 gium is formed of four to seven layers of cells, those near the apex being 

 much thickened, while a band of similar cells passes down the line of 

 dehiscence. A layer of crystal-bearing cells extends inwards from these 

 thickened cells. Stomata occur on the sporangium. The tapetum, 

 which forms a distinct layer in the tetrad stage, is at least partly derived 

 from sporogenous tissue. The output of spores per sporangium increases 

 according to the number of sporangia on the sporophyll. At the time of 

 shedding the pollen-grain contains three cells — prothallial, generative, 

 and tube. 



Pollen Development in Hybrids.^ — R. R. Gates has investigated 

 pollen development in hybrids of Oenothera lata x 0. Lamarckiana, 

 with special reference to mutation. The author disagrees with Pohl as 

 to the failure of pollen development in 0. lata, but regards the cause as 

 inexpHcable. The development sometimes proceeds as far as the tetrad 

 stage, but degeneration always begins then, and may even start as early 

 as the resting-stage. One or two heterochromosomes are formed in the 

 prophase after synapsis ; these do not divide, and probably disappear at 

 the end of the first mitosis. Heterochromosomes are also found in 



* Comptes Rendus, cxliv. (1907) pp. 510-13. 

 t Bot. Gazette, xliii. (1907) pp. 187-20i (1 pi.). 

 \ Tom. cit., pp. 81-115 (3 pis.). 



