50 A MANUAL OF THE PENICILLLA. 



(1935) has reported the terminal conidium in P. bacillosporum to be fairly 

 consistently larger in diameter and of somewhat different shape. Raper 

 and Fennell (1948), in their description of P. levitum n. sp., have likewise 

 noted that the terminal conidium is often substantially larger than other 

 cells in the same chain. There is, however, no evidence that either of these 

 species might represent Corda's P. fieberi. 



Conidia may remain connected in chains of varying length, or may fall 

 away quickly. Chains of conidia may diverge widely, become a tangled 

 mass, stand almost rigidly parallel, or be closely aggregated into columnar 

 masses. In certain species such masses may form continuous crusts cover- 

 ing large areas of the colony. In any case, the same general arrangement 

 of conidial chains in the mass is usually recognizable in successive cultures 

 for each species studied. 



Conidium Formation 



The method of conidium formation (fig. 12): was discussed by Thorn 

 in 1914 and more recently by Scaramella (1928). Thom described the 

 newly formed conidium as at first a cylindrical segment cut from the 

 conidium bearing tube at the tip of the sterigma. It attained the size 

 and shape characteristic of its species by lengthening and swelling, and by 

 the formation of its own cell wall within the primary wall which he re- 

 garded as derived from the parent cell or sterigma. The new wall, or true 

 conidium wall, might blend with the primary wall to leave no visible line 

 of separation, or it might only partially combine with the old wall, leav- 

 ing a bridge or connective easily visible between successive conidia in the 

 chain. Again, also as in Aspergillus, there may be a wrinkling of the old 

 wall to form ridges or spinulose points on the conidium, with or without 

 some deposit of coloring substance between the two walls to give coarse- 

 ness or body to the roughenings or spinulosities. 



Another view, based upon the original discussion by Gueguen (1899), 

 regards, conidium formation as "endogenous," i.e., the separation of a 

 spore mass within a mother cell in such a way that it is allowed to slip out 

 through a tube. Theoretical differences between this process and the 

 above are practically confined to cell wall relations, without seriously 

 affecting the basic observations of either group of workers. In the latter 

 case it is only necessary to assume that the tip of the conidium bearing 

 tube becomes ruptured and somewhat recurved, and that subsequent coni- 

 dia are formed after the establishment of a new membrane or wall adjacent 

 to the inner face of the old tube wall. 



In our experience over many years we have usually found conidium 

 foi-mation to follow closely the pattern described by Thom in 1914 (figs. 

 12A and 12B). Nevertheless, we have occasionally observed preparations 



