SURFACE A.xn MARGIN 01 COLONIES. IT 



that the conidial fructifications are barely raised above the surface, 

 or it may be loose or lax If longer conidiophores give a deeper 

 velvety appearance. 



In the other type all or most of the conidiophores air lateral 

 branches of definitely aerial hyphae. These hyphae and conidiophores 

 form felted masses or loose networks of aerial mycelium for which 

 the term " floccose" is descript ive. 



Margin. In seeking the origin of all structures direct observation 

 of the margin of the young and growing colony is essential. Such 

 observation determines how the fungus spreads in the substratum, 

 theseptatioE and measurement of hyphae, ami t he origin, order of de- 

 velopment, and relative positions of aerial structures. As the colony 

 matures growth ceases, ripe conidial areas extend to the very margin, 

 the masses of conidia often change color and fall apart, and the 

 conidia-bearing branches may curl up or drop off. Some species seem 

 to inhibit their own further growt h after a, short period, while in other 

 cases they dry up the culture medium by transpiring water. Many 

 things thus contribute to render the old colony an unintelligible mass 

 of spores and hyphae. 



In colonies with surface strict or velvety (consisting of conidiophores 

 only I t here i- a succession of structures from the center to the periph- 

 ery. In the center are conidiophores with ripe conidia, marked by the 

 colored area. This shades into a white margin of developing conidio- 

 phores and conidial fructifications, while the extreme margin consists 

 of submerged vegetative hyphae. The relative width of these areas 

 and rate of the development of conidiophores and colored conidia give 

 characterist ic appearances to colonies of part icular species. In some 

 there is a broad submerged vegetative border, then a similar white 

 band of developing conidiophores. In others the area of colored 

 conidia extends so closely to the margin that the white border is 

 barely discernible. In the floccose species aerial mycelium often ex- 

 tends as rapidly at the margin as does the submerged part. In such 



Cases the area of coloration follows the expansion of the colonj more 



slowly. 



Although close resemblances in culture are not uncommon, the 

 relative development of these areas i- quite typical and often sharply 

 distinctive of species. Colonies showing a broad submerged and white 

 margin usually spread over wide areas of the substratum, whereas 

 those bearing ripe fruit to the verj edge of the growing colony rarely 

 develop beyond restricted areas. 



The gross characters already discussed have purely specific value, 

 or ma\ e\cn he more closely restricted as characters distingui hin 

 particular ecads of specie.-. The generic characters and \c\\ impor- 

 tant specific characters are microscopic, and include cell relations and 

 details of spore formation. 

 8108 — Bull. 1 I ^ in -2 



