94 PLECTOMYCETES [CH. in 



The mycelium on which the asci are borne consists wholly or mainly of 

 binucleate cells. The young ascus, as shown by Dangeard in 1894, is at 

 first binucleate; the nuclei soon fuse and the fusion nucleus divides in 

 preparation for spore-formation. 



In Taphrina Cerasi Ikeno in 1903 described the presence, after nuclear 

 fusion, of a densely staining nucleolus or chromatin body as the only nuclear 

 structure in the ascus. A spindle was formed, apparently from the substance 

 of the nucleolus, the remainder of which became the single chromosome. 

 The latter divided by a simple karyokinesis, the spindle was reabsorbed 

 and the process twice repeated to give rise to eight chromatin bodies about 

 which the spores were delimited. In Taphrina Kusanoi and other species 

 Ikeno found no sign of karyokinetic division but the chromatin body under- 

 went successive direct divisions to give rise to eight spore nuclei. 



The nuclei of the Exoascaceae are small and difficult to stain so it is 

 possible that future investigation may modify Ikeno's account ; should it 

 be confirmed it may perhaps be regarded as indicating stages in the dis- 

 appearance of karyokinesis and a useful comparison may be instituted with 

 the similar processes in the Uredinales. 



EXOASCACEAE: BIBLIOGRAPHY 



1887 KNOWLES, E. L. The Curl of Peach Leaves; a Study of the Abnormal Structure 



produced by Exoascus deformans. Bot. Gaz. xii, p. 216. 



1894 DANGEARD, P. A. La reproduction sexuelle desAscomycetes. Le Botaniste, iv, p. 30. 

 1903 IKENO, S. Die Sporenbildung von Taphrina-krtva. Flora, xcii, p. i. 



