ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 9$ 



on the other hand, contains about 35 nuclei, which also divide twice 

 mitotically. While the antheridial tube is still very short, the nuclei 

 of the oosphere all arrange themselves in a peripheral layer of the proto- 

 plasm. This is termed the period of zonation, and the nuclei are then 

 usually in the metaphase stage. About the period of zonation, a central 

 body is formed in the oosphere which the author terms the coenocentrum. 

 It may possibly result from a coalescence of oil-drops, and disappears 

 before fertilisation. During the differentiation of the oosphere the 

 nuclei in the oogone divide once, the mitosis occurring nearly simul- 

 taneously in all the nuclei. The multinucleate or "compound" oo- 

 sphere contains, when completely differentiated, an average of 45 to 55 

 nuclei. 



When the male nuclei enter the antheridial tube, they possess the 

 characters of resting nuclei, but become pointed or fusiform as they enter 

 the oogone. They move through the protoplasm to the female nuclei 

 (the movement being probably chemotropic) and fusion takes place in 

 pairs ; the male nuclei are often somewhat in excess. 



The primitive wall of the " oospore " first appears when the anthe- 

 ridial tube opens. Later the epispore is laid down upon it by the 

 periplasm. Two endospores arc formed by the ooplasm after the develop- 

 ment in the vacuoles of a peculiar substance which disappears as the 

 endospores reach maturity. After the complete encasement of the oo- 

 spore, it becomes rapidly filled with food-materials. The fusion-nuclei 

 pass the winter in the resting condition. 



Reproduction of Saprolegnia.* — Herr G. Klebs makes the following 

 statements respecting the various modes of reproduction of Saprolegnia? 

 derived from the study of S. mixta, a species which grows on the bodies 

 of flies in stagnant water. Multiplication by zoospores, oospores, or 

 gemmae is directly dependent on the external conditions ; there is no 

 regular alternation of sporangial and oogonial generations. From a 

 systematic point of view Saprolegnia is very nearly allied to Sporodinia? 

 while it differs widely both from that genus and from Eurotium owing 

 to its aquatic mode of life. By far the most important factor in deter- 

 mining the mode of reproduction in Saprolegnia is the chemical com- 

 position of the medium, all other external factors — light, oxygen, 

 moisture, temperature — being of subsidiary importance. Formation 

 of sporanges takes place when the growing apices of the hyphae of a 

 mycele are in immediate contact with a medium deficient in nutritive 

 substances, especially in nitrogen and carbon. Oogones, on the other 

 hand, are formed when the entire mycele is subjected to a gradual 

 diminution of nutriment. Thirdly, the gemmae have no well-marked 

 constancy either in morphological or in physiological characters. They 

 are derived partly from the rudiments of sporanges, partly from those 

 of oogones ; but may also be formed from any portions of hyphae that 

 are exposed to very unfavourable conditions of nutriment. 



Fertilisation in the Saprolegnieae.t — Prof. M. Hartog criticises- 

 Trow's paper on the biology of Aclilya, holding that his observations 

 are in many points inaccurate, and maintaining his previous view that 



* Pringsheim's Jahrb. f. wisa. Bot., xxxiii. (1899) pp. 513-93 (2 figs ). 

 t Ami. of Bot., xiii. (1899) pp. 447-59. Cf. this Journal, 1899, p. 515. 



