Fungous diseases of plants . n the jimson weed,{Datura Stramoniuvi). There isalso a very considerable differencein the susceptibility of the differentvarieties of potato, but at present nowholly resistant sorts are known,although the general question ofthe resistance of potatoes to diseasesis receiving special attention in the chief potato-growing regionsof the world. The fungus. Within the tissues the mycelium is light brown toolivaceous, and the conidiophores arise through stomates or push upbetween the collapsed epidermal cells as erect or assurgent fruitinghyphae 50-90 x 8-9/*. They are se
Fungous diseases of plants . n the jimson weed,{Datura Stramoniuvi). There isalso a very considerable differencein the susceptibility of the differentvarieties of potato, but at present nowholly resistant sorts are known,although the general question ofthe resistance of potatoes to diseasesis receiving special attention in the chief potato-growing regionsof the world. The fungus. Within the tissues the mycelium is light brown toolivaceous, and the conidiophores arise through stomates or push upbetween the collapsed epidermal cells as erect or assurgent fruitinghyphae 50-90 x 8-9/*. They are septate, slightly curved, and, asis characteristic of this genus, the conidia are produced singly, sofar as observed, upon the host. The conidia have been describedas obclavate, brown, 145-370 x 16-18/w, terminating in a verylong, hyaline, septate beak (apical cells) equalling fully one-half thelength of the spore (often exceeding this) ; body of spore with 5 to10 transverse septa, longitudinal septa few or lacking (Fig. 137).. Fig. 136. Early Blight of thePotato FUNGI IMPERFECTI 303 The germ tubes arise from any cell of the spore, and it isstated that they may enter the host either by means of thestomates or by directly penetrating the cuticle. This fungusgrows vigorously in pure cultures. Upon prune agar it hasbeen found (Jones) that the spores might be produced as achain of two, and on account of this character the plant hasbeen placed in the related genus Alternaria. As is, of course,well known, the stepfrom Macrosporiumto Alternaria is atbest a very slightone, yet it shouldbe remembered thatthese genera basedupon recognizedlyvariable charactersserve at most forconvenience. Thecatenulate methodof spore productionhas been reportedonly in artificial cul-tures in this case,and it is possible,furthermore, to ob-tain for variousfungi in such cul-tures in generalmany variationsfrom what would be considered the normal type of spore productionupon the host. Attention may be called to
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