INJURIES INDUCED BY PLANTS 147 



A NEW PARASITE OF SEEDLINGS 1 



Seed-beds of the pine and spruce are frequently subject to 

 disease in the months of May and June, so that, even whefe 

 seed has germinated satisfactorily, the plants are more or less 

 decimated, and the otherwise well-stocked drills show blanks as 

 large as one's hand. During wet weather the young plants die 

 and rapidly decay. At first only single plants are attacked, but 

 soon the disease spreads more or less rapidly along the whole 

 drill. If the weather is dry the diseased plants wither, their 

 yellow colour attracting attention even from a distance. During 

 summer, say from the middle of June, the disease ceases, and 

 the dead plants disappear, to leave only the blanks, which are 

 usually ascribed to the ravages of cockchafer grubs, crickets, 

 surface caterpillars, &c. I have shown that in most cases these 

 pathological phenomena are due to Phytopthora omnivora, which 

 spreads not only by gonidia but also by its mycelium, which 

 traverses underground from root to root, and thus explains the 

 rapid spread of the disease. 



In 1889 I received a number of diseased pine seedlings from 

 Herr Mantel, forester in Grossostheim, with the information that 

 for some years a disease agreeing with the symptoms just 

 described had appeared immediately after the germination of the 

 seed in his pine seed-beds on sandy land. Some plants which 

 he sent to the forest school of Aschaffenburg were examined, 

 when it was found that, instead of P. omnivora being the cause 

 of the damage, it was some other unknown disease. 



An investigation of this new disease showed that it was 

 induced by a different parasite. The mycelium of the parasitic 

 fungus which caused the damage attacked not only the seed- 

 lings of the pine but also those of the spruce, alder, birch, 

 &c. In the seed-bed the plants were attacked either at the 

 roots (Fig. 83, a) or at the hypocotyl (), close beneath the 

 surface of the ground. In very dense seed-beds and during wet 

 weather the mycelium also spreads above ground, and infects the 

 cotyledons and the highest part of the stem (Fig. 83, c). At 

 the point where it comes into contact with the epidermis of 



1 Forstlich Naturwissensch. Zeitsch., November 1892. 



L 2 



