Pflanzenkrankheiten. 45 



time during the development of the plum fruit. The hyphae enter 

 through the stomata and lenticeis. Varieties show great differences 

 in resistance to infection, owing to the production of parenchy- 

 matous plugs which fill the stomatal cavity and to lenticeis made 

 up of layers of corky cells through which the hyphae are unable 

 to penetrate. Corkj'' cells lining the stomatal cavity merely delay 

 infection. 



Varieties show variations in resistance to rot after the hyphae 

 have gained entrance, Resistance is apparently correlated with 

 (a) a thick skin; (b) the production of parenchymatous plugs which 

 fill the stomatal cavity; (c) the production of corky walls in the 

 lining cells of the stomatal cavity; and (d) firmness of fruit after 

 ripening. There seeras to be no relationship between oxidase content 

 of the fruit and resistance or between tannin content and resistance. 



Brown-rot is essentially a ripe-rot, afifecting the plums most 

 noticeably as soon as they begin to soften slightly as a result of 

 ripening Varieties which are resistant remain firm on ripening. 

 Softening during ripening is due to the Solution of the middie 

 lamella. 



The hyphae of 5. cinerea in the tissue of plum and apple fruit 

 are entirely intercellular. The middie lamella is dissolved slightly 

 in advance of the penetration of the hyphae. The absence of the 

 middie lamella in fruits which have softened owing to ripening 

 explains the greatly increased spread of the disease at ripening 

 time. Attempts to demonstrate the presence of the middle-lamella- 

 dissolving enzym, pectinase, in rotting fruits or to extract it from 

 a culture of the brown-rot fungus on apple eider proved futile. 



The rot caused by 5. cinerea is a firm-rot due to the mechanical 

 Support of the hyphae which completely fill the intercellular Spaces 

 left by the collapse of the host cell walls. Penicillium expansutn 

 produces a soft-rot, because of the fact thatfew hyphae are produced 

 and, therefore, little mechanical support is given to the rotted 

 tissue, which as a consequence collapses as the rot proceeds. The 

 hyphae of P. expensum are intercellular and produce a substance 

 which dissolves the middie lamella even in the absence of the 

 fungus hyphae. Jongmans. 



Weip, J. R., Wallrothiella arceuthobi. (Journ. Agric. Research. IV. 

 p. 369-378. PI. 55, 56. 1915.) 



Wallrothiella arceuthobi, a fungous parasite on the false mistle- 

 toes of conifers, is reported for the first time in the West. This 

 fungus was considered a very rare species until it was found to 

 be of common occurrence in parts of Montana and Idaho. 



Several new facts pertaining to the morphology and general 

 behavior of the fungus are established. 



Its host ränge has been greatly extended. 



The significant fact that the fungus is found in the West on 

 those forms of species of the same genus which are most similar 

 to the eastern blackspruce mistletoe, its host in the East, is thought 

 10 have some bearing on the taxonomic position of this particular 

 group of mistletoes. 



Its parasitism on the false mistletoe is found to be of great 

 significance in the control of these parasites, which are so destructive 

 to many western conifers. Jongmans. 



