70 Varietäten etc. — Physiologie. 



14 (two rings of 7 each) typically in the B variety. The number is 

 never greater than 10 in the former but may be sometimes less 

 than 14 (though more than 10) in the latter. The capacity to in- 

 crease the number of bundles beyond 10 behaves as a simple 

 dominant to absence of such capacity. 



4) As regards habit and foliage, crossing leads to the production 

 of a number of new typus in F 2 . Segregation occurs involving the 

 reappearance of the original characters of the grand parents. Diffe- 

 renoes relating to these features have not been adequately studied 

 for complete analysis, but it is believed that the number of factors 

 concerned in the determination of leaf shape is small, possibly two. 



The authors point out the bearing of these experiments on the 

 subdivision of existing species of plants as emphasising the need 

 of caution where breeding tests have not been carried out. 



No experimental proof was obtained that parthenogenesis occurs 

 nor was any fertile seed obtained as the result of numerousattempts 

 to cross B. dioica with other members of Cucurbitaceae. 



W. Neilson Jones. 



Blackmail, V. H. and E. G. Welsfoi'd. Studies in the Phy- 

 siology of Parasitism. II. Infection by Botrytis cinerea. 

 (Ann. of Bot. XXX. p. 389—397. 1 pl. 1916.) 



The authors studied microscopically the details of infection by 

 Botrytis cinerea. The spores were grown in drops of turnip juice 

 on the leaf. The germ-tube produced from the spore possesses a 

 mucilaginous sheath, by means of which it becomes firmly fixed to 

 the surface of the leaf. Penetration takes place by the development 

 of a fine, peg-like outgrowth from that part of the germ-tube which 

 is firmly pressed against the leaf-surface. 



Prior to the penetration of the cuticle no softening, nor swel- 

 ling, nor any other change can be observed in the cuticle itself or 

 in the underlying layers of the epidermal wall. The piercing of the 

 cuticle is brought about solely by mechanical pressure, which is 

 rendered possible by the fixing action of the mucilaginous sheath 

 of the germ-tube. 



After penetration enzyroe action occurs, as is shown by the 

 swelling of the subcuticular layer. 



There is no microscopic evidence for the secretion by B. cine- 

 rea of a special toxic substance other than the cell-wall dissolving 

 enzyme. E. M. Wakeneid (Kew). 



Brown, W., Studies in the Physiology of Parasitism. III« 

 On the Relation between the „Infection Drop" and the 

 underlaying Host Tissue. (Ann. of Bot. XXX. p. 399— 406. 1916.) 



This paper is supplementary to N° II of the same series, by 

 Blackman and Welsford. The author has studied the action of 

 the infection drop and of extracts of Botrytis cinerea on the leaf. The 

 germ-tubes are unable to affect chemically the cuticle of the host, 

 nor do they secrete any toxic substance which can pass through the 

 cuticle and bring about the death of the underlying cells. Penetra- 

 tion must therefore take place in a purely mechanical way. Once 

 penetration of the cuticle has been accomplished, the underlying 

 tissue is attacked as described in N° I of this series of papers. 



E. M. Wakeneid (Kew). 



