MONOGRAPH OF THE LABOULBENIACEiE. 



239 



which under abnormal conditions may be replaced by or associated with typically fila- 

 mentous growths similarly derived from the basal cells. 



In very rare instances individuals are met with in which a typical antheridial ap- 

 pendage, in a normally bisexual form, is substituted for the female organ, the 

 substitution being accompanied by a great increase in the number of antheridia pro- 

 duced. An abnormal male individual of this kind is represented in Plate II, fig. 7, the 

 two appendages being in general normal even to the formation of the blackened in- 

 sertion cells. 



We have seen that in general the spores are discharged in pairs, and that, as a 

 rule, and sometimes invariably, they adhere to the host and develop side by«ide. It 

 is an interesting fact which may possibly have some bearing on the derivation of the 

 dioecious from the monoecious forms, that in certain instances one member of the spore 

 pair may normally, or not infrequently, become atrophied, or produce a smaller and 

 weaker individual than the other. In the case of Laboulbenia inflata the atrophy of 

 one of the spores, after it has reached an inconsiderable development, seems to be an 

 invariable rule, as far as I have had an opportunity for observation, and groups of 

 this species, when detached with a portion of the integument on which they are 

 growing, show the condition of things represented in fig. 5, Plate III, the atrophy 

 being apparent even at an early stage. 



Normal Variations. Like other groups of plants, the Laboulbeniacete are subject 

 to normal variations in form, size, color, etc., which are partly inherent and partly 

 due to the action of external causes. In individuals growing under identical con- 

 ditions, the variations are comparatively slight, and are expressed by inconsiderable 

 differences in gross size, or variations in the relative development of different parts, 

 often coupled with differences in color, which are, however, in general, due to the 

 varying age of individuals. Forms, for instance, which, when young, even when they 

 are sufficiently advanced to discharge their spores, are hyaline or pale straw-color, 

 may become, as their age increases, dark amber-brown or suffused, wholly or in part, 

 with blackish or smoky-brown shades. 



Among the external causes which influence variation, the most important are 

 associated with the character of the host, its size, and the position in which the para- 

 site grows upon it. The color of the host, for example, often influences that of the 

 parasite, the same species being sometimes very dark or nearly opaque on hosts with 

 a dark or black integument, while they are pellucid, or nearly hyaline, on hosts of a 

 lighter color, such differences in color being independent of differences in the age of 

 the individuals in question. 



