MORPHOLOGY AND DESCRIPTION 25 



number and dimensions of such. Such conidia may be very thin-walled, 

 delicate and readily destroyed, or firm-walled, almost impervious to stains 

 and able to retain their vitality for many years. They are extremely small, 

 light, and float readily in air currents. In many species, the outer layer of 

 the spore wall absorbs water slowly, hence such spores tend to float in 

 currents of fluid or to develop as mycelia covering the surfaces of liquid 

 media. Molds being typically aerobic, normal colonies develop only on 

 the surface of the substratum where oxygen is abundant and their spores 

 can be discharged directly into the air. Spores developing under submerged 

 conditions in the absence of adequate oxygen produce fragmentary and 

 defective mycelia only. 



The "Connective" 



Descriptive literature often cites the presence of a "connective" or 

 "disjunctor", a "bridge" between conidia in the chain. This is sometimes 

 present, again absent, in the same microscopic preparation, and when 

 seen, it appears as a short space between spores, bridged by transparent 

 cell walls. This is exactly what it is. Cells cut off from a cylindrical 

 tube may swell and assume subglobose form without breaking their area 

 of contact, or, in the swelling and rounding up process, they may partially 

 or completely break that contact leaving the original cell wall of the tube, 

 within which they developed, as a bridge across the open space (fig. 64 C). 

 The critical examination of the developing cells in thousands of preparations 

 have failed to justify interpretations which assume the degeneration of 

 every alternate cell, or fantastic fusions in the production of conidia. The 

 observation of connectives is, therefore, ordinarily worthless because 

 morphologically it means nothing, and it is not justified by successive 

 studies of the same species. 



Endogenous Conidia 



A spore is described as endogenous if it is formed within a tube or cell 

 wall of a previously existing cell. It may be extruded through a tube. 

 That tube may be used once only or many times. The critical factor 

 is the formation of a cell or spore within an existing specialized spore- 

 bearing organ and its extrusion from that body through a fixed tube. In 

 Aspergillus, the tip or tube of the sterigma elongates, a cylindrical section 

 is cut off carrying the tube wall and the septum at each end as the primary 

 wall of the spore itself. Within that primary wall the spore as an entity 

 rounds itself up to characteristic form, deposits or lays down its own wall 

 with whatever coloration or markings may be typical of the species. The 

 primary wall may remain separate and distinct and in the ripe spore be 

 visible under the microscope, it may be blended with the secondary wall, 



