580 THE FUNGI WHICH CAUSE PLANT DISEASE 



Numerous studies ^'*^ of the power of B. cinerea to infect growing 

 tissue have been made with the conclusion that it is a weak parasite 

 and that to become aggressively parasitic it must first develop 

 a vigorous mycelium saprophytically. Attempts to immunize 

 plants against its attack have been made with partial suc- 

 cess.**^ 



Extensive studies of the condition of sclerotia and conidia forma- 

 tion by B. cinerea (from grape) were made by Reidemeister.^^^ 

 He concludes that sclerotia form on all media favorable to growth 

 of the fungus. They are on an average 5-8 mm. in diameter, 

 smaller under conditions of poor nutriment, high osmotic pressure 

 or strong transpiration. They are often found in concentric rings 

 and their formation is induced by the presence of various agents 

 which inhibit growth. Conidia are formed imder condition of 

 energetic transpiration and on media of high osmotic tension. 

 Conidia and sclerotia vary inversely in production. Appressoria 

 develop on all media where sclerotia grow and are favored by 

 substances which inhibit growth. Conidia are suppressed by 

 conditions favoring the formation of appressoria. 



B. deprsedens Cke. is a pest of the sycamore. 



B. fascicularis (Cda.) Sacc." 



Cespitose, minute, brownish; hj^phae erect, fasciculate, flexuose, 

 brown, or semi-pellucid, branches hyaline; conidia in subglobose, 

 white heads, oblong, large. 



A mold of egg-plants is attributed to this fungus by Hal- 

 sted. 



An undetermined Botrytis is reported on carnation by Atkinson 

 and another on Ribes.^^^ 



B. parasitica Cav. 



Hyphse cinereous, sparse, erect, inflated at base; conidia ovate, 

 large, short-pedicillate, on short branches, heads umbellate, hya- 

 line or dilute, cinereous, 16-20 x 10-13 n. 



This is said by Halsted " to be the form found on lilies, parti- 

 cularly the bulbs, in New Jersey. It was first reported by Cavara 

 in Italy and is widespread and destructive. 



B. pceonise Oud. ^^' *«• "^^ 



Mycelium in the parenchyma of the host, hypha erect, 0.25- 

 1 mm. high, protruding through the stomata, branches spirally 



