24 



A MANUAL OF THE ASPERGILLI 



The Conidium, or Spore 



The conidia are thus specialized propagative cells, asexual in origin, 

 produced by a complex cellular fruiting structure. This consists (1) of a 

 foot-cell connected with the vegetative mycelium and usually imbedded 

 in the moist substratum, (2) of a conidiophore, or stalk, rising more or less 

 vertically into the air to a distance typical of the species and enlarged at 

 the apex to form the vesicle which is the central unit, and (3) of a dilated 

 head consisting of one or two series of cells, the outermost of which are 

 specialized for the purpose of producing chains of cells (the conidia), 

 each equally capable of carrying the genetic factors necessary to propagate 

 the species. 



Fig. 6. Camera lucida sketches showing progressive stages in conidium formation, 

 X 700. A, Initiation of conidium formation. B, Secondary sterigma bearing a 

 chain of three conidia, the outermost developing characteristic roughenings by the 

 deposition of coloring matter between the outer (thin) and inner (firm) wall. C, 

 Sterigma bearing a chain of conidia in which differentiation of the outermost spore 

 is complete. D, A single mature conidium seen in surface view. See discussion on 

 page 24. 



After the conidium is separated by a septum from the mother cell or 

 sterigma, it remains so attached 1 as to draw nutrients from the parent 

 cell at first, while it assumes the size and shape characteristic of the species, 

 then it lays down within its original, or primary wall, a secondary cell wall 

 whose color, texture, and marking are those of the species. The secondary 

 wall completely separates this spore from the parent cell. (fig. 6). Exact 

 uniformity is not attained. An occasional cell fails to develop; some differ- 

 ences in size are usually evident; markings, while characteristic in nature 

 and general pattern, are not always identical as to details. For descriptive 

 purposes, size ranges are therefore more important than exact measurements 

 and the nature of the markings found are more important than the relative 



1 Buller (Researches on Fungi V, Chapter II, 1933) discusses the primary septum 

 as having a central pore through which connections are maintained. 



