440 SUMMARY OF CURRENT RESEARCHES RELATING TO 



0. LamarcTciana, and probably represent discarded chromosomes, and 

 this may be a means of lessening the number of chromosomes in 

 certain germ-cells of the species. Extra nuclei are found in the 

 cytoplasm, in the tetrad divisions of the hybrid 0. lata, and this seems 

 to disprove the purity of other plants, e.g., HemerocalUs fidva, where 

 they also occur. It is probable that the mutations of 0. Lamarckiana 

 arise during reduction division, and that the pollen-grains which give 

 rise to mutants difiFer greatly from ordinary pollen-grains. The author 

 beheves that a cytological basis may be found for the phenomena of 

 mutation in CEnoihera. 



Ovule of Dioon.* — C. J. Chamberlain has investigated the ovule 

 and female gametophyte of Dioon. The specimens examined occur 

 abundantly in Mexico, and the plants probably attain the age of over 

 lOOO years. The ovulate strobilus is loose, resembling that of Gijcas, and 

 the megasporophylls are also leaf-like. There is a three-layered integu- 

 ment, probably derived from two original integuments ; only a small 

 part of the nucellus is free. One vascular bundle from the sporophyll 

 supplies the ovule, and sends out branches to the inner and outer layers 

 of the integument. There are usually 4-5 archegonia, but the number 

 varies. Each archegonium makes its appearance in October, when the 

 neck and central cells are formed ; the ventral canal and egg nuclei are 

 not formed until the next May. The Qgg nucleus has 12 chromosomes, 

 this being the largest number known in plants. The central cell and 

 the Qgg are nourished in the usual way during the earlier stages, but 

 later on the food is suppUed through haustoria which pass from the egg 

 directly to the cytoplasm of the jacket-cells. 



Development of Ovule in Ginkgcj — I. E. Carothers contributes 

 the results of her investigations upon the development of the ovule 

 and female gametophyte of Ginkgo. The nucellus has a large beak, 

 and the sporogenous tissue is deeply seated. There is usually only one 

 mother-cell, and this has a peculiar kinoplasmic mass. The gameto- 

 phyte has H chromosomes. The lowest spore is the functional one, 

 and is vacuolate, with parietal, free nuclei ; later on walls are formed 

 centripetally between these nuclei, until the sac is filled with cells. 

 These cells have their inner ends open, and are sometimes uninu- 

 cleate, more rarely multinucleate ; when the growing cells meet at the 

 centre each forms an end wall. The outer wall of the prothallium is 

 thickened, while the inner wall of the megaspore is a thin, firm layer, 

 surrounded by a very thick outer layer. The archegonia develop while 

 there is still a large central cavity. The gametophyte has much chloro- 

 phyll. Around the mother-ceil is spongy tissue, which acts as a 

 tapetum. The integument is soon differentiated into three coats : outer 

 fleshy, middle stony, and inner membranous, and two special bundles 

 bring an abundant supply of liquid to this inner layer. 



Embryogeny of Cuban Nymphaeacese.l — M. T. Cook has investigated 

 the embryogeny of Brasenia purpurea, Cahomha piauhiensis, and other 



* Bot. Gazette, xlii. (1906) pp. 321-58 (3 pis. and 9 figs.), 

 t Op. cit., xliii. (1907) pp. 116-30 (2 pis.). 

 % Op. cit., slii. (1906) pp. 376-92 (3 pis.). 



