ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 193 



between the centrosomes ; the two chromosomes then divide longitudi- 

 nally. They then move towards the poles, and reunite into a chromatic 

 mass which masks the centrosome, and from which the rays of the 

 aster now seem to radiate. The spindle soon disappears, and the second 

 division commences almost immediately. This takes place in the same 

 way as the first division ; the four centrosomes appear to determine the 

 formation of the four spores. 



The same process takes place in the other genera, with slight modifi- 

 cations. 



Boring Growth and the Abnormal Formation of Conids in Dema- 

 tium pullulans.* — A. Klocker ami H. Schionning state that their re- 

 searches lead to the conclusion that the phenomena of boring growth 

 are of frequent occurrence in Dematium pullulans de Bary and in certain 

 species of Oidium, just as happens in many other fungi. Conids are 

 formed within certain cells, and the conditions for the formation of these 

 conids are defective nutriment and too much air and moisture. True 

 endospores are not formed in these corpuscles, as Weleminsky asserted, 

 and his inference that Dematium pullulans should be placed among the 

 Ascomycetes f near to Saccharomyces and Exoascus was wrong. 



Dematium pullulans should, as heretofore, be classed with " Fungi 

 imperfecti." Like Weleminsky, the authors had no success in their 

 endeavour to discover a geuetic relation between Saccharomyces and 

 Dematium. 



Endotrophic Mycorhiza of Neottia nidus-avis. % — Werner Magnus 

 has made an exhaustive study of the mycorhiza of the birds'-nest orchis, 

 which differs in several points from that of other Orchidese. 



In the root it is exclusively the 3-4 outermost layers of cells beneath 

 the exoderm that are infected ; in the rhizome and aerial stem as many 

 as six layers may be attacked. In the root-cells the fungus is differen- 

 tiated into two perfectly distinct forms, with no transitional grades. In 

 the " host-cells " (Pilzwirthzelle) the fungus exhibits no degeneration ; 

 thick-walled hyphse run along the cell-walls, and send out finer thin- 

 walled hyphse which traverse the entire cell and are adapted for nutri- 

 tive purposes. In the " digestive cells " ( Verdauungszelle) the fungus is 

 always degenerated ; thin-walled hyphae rich in protoplasm permeate the 

 cell in dense balls, which die, and the contents of the hyphae are ab- 

 sorbed and digested by the cell, leaving a perfectly indigestible and un- 

 changeable residue, which becomes transformed into a cellulose-like 

 substance. The digestive cells occupy the outer and inner, the host- 

 cells the central layers. In the rhizome there is not the same regular 

 differentiation. A third symbiont, a parasitic fungus (undetermined), 

 lives on the undigested residue. 



The protoplasm forms a continuous layer round the fungus in the 

 cell, and is copiously renewed. The digestive cells seem to serve ex- 

 clusively for the nutrition of the more highly organised of the two 

 6ymbionts ; the host-cells for that of the fungus-symbiont, which carries 

 on in them a parasitic existence, and forms organs which can hibernate 

 outside the plant. 



* C.R. Trav. Laborat. Carlsberg, v. (1900) pp. 47-57 (6 figs.). 



t Cf. this Journal, 1899, p. 520. 



% Pringsheim's Jahrb. f. wiss. Bot., xxxv. (1900) pp. 205-72 (3 pis.). 



April 17 th, 1901 O 



