1919] DISEASES OF PLANTS. 545 



before the first symptoms appear, ami during the growing season when the 

 fungus is active. 



Seedling- diseases of conifers, C. Hautlev, T. C. Mkkkiu., and A. S. Rhoaijs 

 (Jour. Agr. Research, [U. S.], 15 (1918), No. 10, pp. 521-558. /,/. /).— According 

 to the authors, damping-off of coniferous seedlings is an important factor in 

 the propagation of these trees, and the fact that a number of damping-off 

 parasites are able to cause practically identical symptoms has led to a study 

 both of damping-off and of other diseases which may attack seedlings of the 

 same age. The present paper, a contribution from the Bureau of Plant Industry, 

 U. S. Department of Agriculture, gives an account of the diseases which the 

 authors found attacking seedlings up to the age of approximately two months. 



Corticium vayum, Pythium thbaryanum, and other oomycetes; Fusarium moni- 

 liforvie, F. vetitricosum, F. solani, and other species of Fusarium; Trichoderma 

 spp. ; and Butrytis cinerea have been isolated from damped-off conifers and are 

 believed to cause the disease. Artificial inoculation on pines in autoclaved 

 soils showed that the first three species were specially virulent parasites, and 

 all except Trichoderma spp. gave more or less indication of parasitic ability 

 in inoculation experiments. 



For V. vayum, 12 coniferous hosts are listed. One strain of the organism 

 was maintained in artificial cultures for eight years without perceptible loss 

 of virulence. Marked differences in virulence between different strains were 

 observed, but this is considered to bear little relation to the host from which 

 the strain was isolated. There was no indication observed that passage through 

 seedlings and ivisolation resulted in any increase in virulence. C. vayum was 

 found especially virulent in inoculations on sandy soils treated with sulphuric 

 acid followed by lime. With the possible exception of P. debaryanum, C. vayum 

 Is considered the most important single damping-off parasite on conifers. Cer- 

 tain species of Fusarium are also believed to be important, while the remainder 

 of the organisms mentioned above are rather unimportant. 



Lists are given of other species of fungi winch are observed in connection 

 with damping-off of seedlings, but most of them were either weakly parasitic 

 or present as saprophytes. 



A large amount of the damage done by C. vayum and P. debaryanum is 

 caused by the killing of the seed or seedlings before they appear above ground. 

 such losses being often attributed to poor seed. Strains of Fusarium are 

 less inclined to attack seedlings in this manner. Excessive heat, drought, 

 or bending over may cause damage closely resembling damping-off, but this type 

 of injury may usually be distinguished from the parasitic attack. 



Parasitism, morphology, and cytology of Cronartium ribicola, R. H. Collet 

 (Jour. Agr. Research [U. S.), 15 (1918), No. 12, pp. 619-660, pis. 12, fig. 1).~ 

 Results are given of studies on the parasitism, morphology, and cytology of 

 C. ribicola, the investigations having been carried on in the Bureau of Plant 

 Industry, U. S. Department of Agriculture. Considerable unpublished data are 

 reported on the morphology and cytology of C. ribicoln. and the Interrelations 

 of the parasite and its hosts, Pinus strobus and Ribet spp., are described. 



The mycelium of the fungus is said to be more abundant in P. strobus than 

 in species of Ribes, and in the former host the hypa? force the cortex and phloem 

 cells apart, thus causing a swelling of the infected bark. The destructive 

 effect on the pine host resulting from the attack of C. ribicola is said to vary. 

 In young trees death may result quickly, while in older ones the attack is in 

 the nature of a primary injury winch may prepare the way for the drying 

 out of the infected bark and the entrance of secondary fungi and insects which 

 complete the destruction initiated by the fungus attack. The effect on Ribes 



