56 PLANT DISEASES 



PREVENTIVE MEANS. This disease only occurs where 

 the ground is very wet and the light dull. If seed beds 

 are formed where the drainage is good, and a fair share of 

 sunshine allowed, the fungus is completely held in check, 

 as its reproduction and diffusion depend entirely on the 

 constant presence of water in the soil. 



De Bary, Bot. Ztg. 1881, p. 357, Tab. 5, figs. 1-7. 



Marshall Ward, Quart. Journ. Microscop. Sci., vol. xxiii. 

 (1883), p. 487, pi. 24, figs. i-io. 



Massee, Brit. Fung., p. 133, pi. 3, fig. 39. 



DAMPING-OFF PKOTHALLIA 



(Pythium intermedium, De Bary.) 



Dr. George F. Atkinson detected this fungus on fern 

 prothallia in the botanical conservatories of Cornell 

 University, U.S.A. The affected prothallia were quite 

 soft, limp, and darker in colour than the healthy ones. 



' If the pots or vessels in which the prothallia are grown 

 are rested in sphagnum, a layer of which can be placed in 

 the bottom of the wardian case, and after the young pro- 

 thallia have started, all the watering be applied through 

 this, the prothallia will do much better than if surface 

 watering is practised, and far better than where the pots 

 are rested in a vessel partly full of water. The air of the 

 wardian case or of the house should not be kept too damp.' 



Atkinson, Bull. 94, Cornell Univ. Agric. Expt. Station, 

 p. 247, i plate. 



This Bulletin contains valuable information on the 

 life -history of other allied species, and is beautifully 

 illustrated. 



