OBSERVATION AND DESCRIPTION OF PENICILLIA 



49 



tire developing cell. Although conidia in certain species have been de- 

 scribed as globose at first, becoming elliptical in maturity, no evidence of 

 this condition has been seen by us. The individual conidium usually 

 attains the characteristic size, shape, and markings for a given species 

 by the time a half dozen newer conidia have been cut off between it and the 

 sterigma. Thereafter, walls may thicken somewhat and markings maj'' 

 become more accentuated, but otherwise little visible change occurs irre- 

 spective of the time the conidium may remain attached in the chain. 



Fig. 12. Conidium formation in Penicillium. A, P. digitatum Saccardo: A\, 

 Camera lucida drawings of sterigmata and attached conidia; Ai, Diagrammatic 

 representation of conidium formation. B, P. ■pur-purrescens (Sopp) n. comb.: jBi, 

 Camera lucida drawings of sterigmata and conidia; 1?2, Diagrammatic representation 

 of conidium formation in the same species. C, A type of conidium formation occa- 

 sionally seen in various Penicillia and usually observed, as shown, in a strain, NRRL 

 1129, assignable to P. tardum Thorn: C\, Camera lucida drawings of sterigniata show- 

 ing origin of conidia from cup-like tubes; d, Diagrammatic representation of this 

 type of conidial origin, a, Conidium bearing tube of sterigma; h, Young conidium 

 in formative stage; c, Connective, disjunctor, or bridge consisting of an extension of 

 the primary wall from one conidial cell to the next; d, Secondary, more or less thick- 

 ened wall; and e. Primary wall closely applied to secondary wall in A-i and d, in B^ 

 it becomes pushed out somewhat as coloring substance accumulates between the 

 outer (primary) and inner (secondary) walls. See discussion in text. 



Corda, in describing and illustrating his Penicillium fieheri, specified 

 that the oldest (or end) conidium of the chain, and sometimes the second 

 oldest conidium, was much larger than the others. This condition has 

 seldom been reported by subsequent workers although Biourge reported 

 the "phenomenon of Corda" for a few species. Thom (1930) observed, in 

 a culture belonging to the P. brevi-compadum series, a condition which he 

 thought probably constituted the basis for Corda 's interpretation. Drops 

 of fluid were exuded at various points in the penicillus and along the 

 conidial chains in such a way that the conidia at the very tips seemed to 

 be much larger than those subsequently developed. More recently Swift 



