



SPECIES OF CHOANEPHORA. 



165 



Th 



species is certainly capable of parasitic existence on other hosts than Ip 



rubro-cvrulea. The conidia or sporangial spore, when sown on the petals of 4IW _ a 

 Zinnu* elegans and kept in a moist atmosphere germinate freely, giving origin to germinal 



tubes which 



, *c , P en f trate the *»*» and very rapidly cause their death, producing a crop of 

 fruchncation wnieb, although not so vigorous as that occurring on Ipomva rubro-c<rnd<a, 

 is still of conidial type. In this it differs from Choanephora Cunning hamian a tin- conidia 

 or spores of which when sown on Zinnia-flowers fail to give rise to any blighting of 

 the latter. As I have more than once observed Zinnias affected by what on casual in- 

 spection I took to be Choanephora Cunninghumiana, there can be little question that, these 

 flowers occasionally play the part of natural hosts to the other species. 



The diffusion of the blight in Ipomaa rubro-cosruka seems to be mainly determined 



direct contact with previously affected tissues, blighted portions of axes 



g as 



sources of infection of adjoining healthy ones, and the adhesion of blighted and wilted 



the 



healthy ones or to healthy axes being followed by the appearance of the di 



In artificial cultivations, whether in infusions of Ipomcca ruhoccerulea or of the 

 flowers of Hibiscus rosa-sinensis, the conidial fructification is ordinarily entirely sup- 

 pressed, and, when it does make its appearance in connection with greatly concentrated 

 media, it is only feebly developed. Very few heads of normal type are developed, and 

 these at utmost bear a very limited number of capitella. In most instances the conioia 

 arise directly from the primary capitulum, or even this is suppressed, and they arise 

 simply from the undilated tip of the stem, or at short intervals from one another in its 

 neighbourhood, so that the fructification comes to present an almost peronosporic 

 character ^Plate IX, Fig. 10). In certain cases only a single terminal conidium may 

 be present (Plate IX, Fig. 10). 



When cultivated in infusions of the leaves of Ipomcea rubro-cccrulea or of the 

 flowers of Hibiscus rosa-sinensis of moderate strength, or on boiled petals of the latter 

 plant, sporangic fructification is developed in great abundance, either alone or associated 

 with varying numbers of zygospores, and it is only in extremely concentrated infusions, 

 specially of Hibiscus y that conidial fructification also begins to make its appearance 

 in association with the sporangic one. The abundance of sporangia produced in culti- 

 vations in media of average quality is excessive. Under normal circumstances they 

 are produced in far greater numbers and attain a much greater size than those of 



Choanephora Cunning hamiana ever are or do (Plate VIII, Figs. 3, 20; Plate IX, Fig. 



15). At an early stage of development they are of an amber colour owing to the tint of 

 the sporangic membrane, but on ripening they become first brown and ultimately almost 

 black owino- to the dense accumulation of the brown spores which are formed within 



o 



them (Plate VIII, Figs. 3, 20). The stem is ordinarily abruptly flexed immediately 

 beneath the origin of the sporangium, so that the latter looks more or less downwards. 

 On maturing, the sporangia dehisce in valvular fashion allowing the spores to escape, 

 whilst the two halves of the membrane remain attached to the tip of the stem on 

 either side of the large columella. (Plate VIII, Fig. 19). The sporangic membrane is 

 ordinarily finely tuberculate. 



The spores are very peculiar. Like the conidia they are fusiform in outline and 



provided with a finely striate brown epispore (Plate IX, Fig. 2). They have average 

 dimensions of 0'0168 X0'0089 m.m., and are therefore relatively somewhat narrower 

 than the conidia, and the brown tint of the epispore is as a rule somewhat deeper than 



Ann. Koy. Bot. Gaed. Calcutta Vol. VI. 



