ENTOMOPHTIIORKAK OF THE UNITED STATES. 



I 13 



to a single conidium. In the second instance, where the external growth is greater, a 

 different type usually occurs in the conidiophores. Not only is the external branching 

 very considerable, but the ultimate divisions of each conidiophore are arranged in a co- 

 rymbose or digitate fashion, as in figs. 202 and 220. This occurrence of simple and 

 compound conidiophores in different species has led to the generic separation of the two 

 groups; yet the distinction is by no means absolute, and intermediate forms occur, as in 

 E. culicis, E. apiculatus and a few additional species. The converse is also true, and 

 simple conidiophores are very commonly found in species where the type is usually com- 

 pound. As has been already remarked, the growth of conidiophores is very rapid under 

 favorable conditions; and an insect containing hyphal bodies, if placed in a damp, warm 

 atmosphere, may give rise to the characteristic white masses in a few hours. Soon after 

 the appearance of these masses the production of conidia commences, and this brings 

 us to the next step in the conidial development. 



Formation and discharge of the conidia. — The terminal portion of the conidiophore, 

 whether this be simple or one of several digitations, is termed the basidium and is usu- 

 ally swollen to a greater or less extent. From the apex of this basidium, which is ho- 

 mologous with similar structures occurring among the Mucorini, the conidium, or more 

 properly the mother cell of the conidium, is formed by budding. This bud increases 

 at the expense of a portion of the contents of the basidium, until it has attained very 

 nearly the normal shape and dimensions of the conidium; when it becomes separated 

 from the basidium by a cross partition, which forms at first a horizontal plane of separa- 

 tion between the two and is homologous with the columella of the Mucors. Within the 

 mother cell thus formed is developed a single conidial spore, the walls of which are nor- 

 mally in close apposition to those of its containing cell, which must thus be considered 

 a sporangium reduced to its simplest terms and modified to combine economy of material 

 with a judicious dissemination. The resemblance to a one-spored sporangium is clearly 

 seen in cases where, through the absorption of water by osmosis, the wall of the mother 

 cell becomes separated from that of the conidium; a phenomenon which is very com- 

 monly seen after, or even before, the discharge of the conidium, and is sometimes carried 

 to such an extent that the conidium may be seen floating free in a large spherical 

 mother cell (fig. 321). 



When the conidium is fully developed, and even previous to this, the contents of the 

 spore, as well as of the basidium, begin to expand through the absorption of water. 

 At first, as a rule, the contents of the basidium exert the greater of the two forces thus 

 produced ; perhaps owing to the fact that a more rapid absorption of water is possible 

 through its single wall than through the double wall of the conidium. For this reason, 

 the columella is at first forced outwards into the conidium towards which its convexity 

 is thus turned. In some instances, especially in cases where the basidia are large and 

 strong, this condition of things may continue until the discharge of the conidium. 

 Such is apparently the explanation of the appearance figured by Nowakowski 1 which is 

 referred to by Eidam 2 as a mechanism for discharge, very different from that usually 

 found in Empusae. I think, however, that this will prove to be only an extreme case of 

 the nature just described. In my own experience I have observed this appearance only 



1 J..c. B, PI. xr, fig. 82, etc. s I. c, p. 186. 



