66 A MANUAL OF THE ASPERGILLI 



throw out branches which fuse without showing any other sign which might 

 suggest a sexual process either before or after fusion. Anastomosis is 

 usually observable, if at all, in the rapidly growing area where many spores 

 placed as an inoculum are developing into one colony. By transferring 

 large numbers of spores from an old culture to a new one, most of the 

 Aspergilli studied by us have shown fairly consistent repetition of colony 

 characters and conidial morphology and have been maintained for a long 

 time with little or no observable change. Other organisms handled in the 

 same manner have not been successfully maintained with the morphology 

 originally studied. Differences in behavior can be attributed to variability 

 between strains. 



Intra-species Variation 



Variation within the species is very prevalent and is well marked in many 

 cases. When a large number of isolates of any particular species or series 

 is collected, one can regularly expect to find among them wide variations in 

 color, amount of sporulation, and in their general habit of growth. Usually, 

 however, such variation is graduated, and strains representing various 

 intermediate steps between the extremes are to be expected. While it is 

 by no means unique, we may use A. terreus as an example, since a very large 

 number of strains belonging to this species have been isolated and observed 

 in plate and tube cultures during the past two years (fig. 16). Colonies of 

 the type strain, and of the great majority of isolations made from nature, 

 are plane, cinnamon in color, very heavy sporing, with conidial heads arising 

 directly from the substratum in an even and close stand. An occasional 

 isolate is much brighter in color, approximating xanthine orange (Ridgway, 

 PL III), but in all other respects it is fairly typical. It is believed to repre- 

 sent a form such as that described by Blochwitz (1934) as A. boedijni, and 

 in the present manual we have designated it as A . terreus var. boedijni. In 

 each of the above cases, the production of abundant fruiting structures 

 follows closely the advancing margin of the growing colony and there is little 

 or no continued growth of mycelium except in the marginal area. Certain 

 other strains are quite floccose; conidial heads are typical in form and color 

 but are greatly reduced in number and are borne upon aerial hyphae. Shih 

 (1936) was probably working with such a culture when he described the 

 variety A. terreus var. floccosus. We feel that the forms are sufficiently 

 distinct to warrant maintaining his variety. Still other strains possess 

 abundant but fairly close-, rather than loose-textured mycelia and bear 

 abundant but very pale buff-colored conidial heads. The vegetative my- 

 celium in this form is bright yellow and for this reason we have designated it 

 as A . terreus var. aureus n. var. (see p. 198) . If one should examine only the 

 type strain and these three atypical forms, it is entirely probable that one 



