THE GENUS ASPERGILLUS. 307 



with the Microsporecv, the limit being fixed at 5 /x. In contrast 

 to the conidia formed by successive constrictions of the tips of the 

 sterigmata, and sometimes connected by delicate " intermediate 

 cells," the primary sterigmata are formed by protrusions from the 

 surface of the globule, sometimes before the stem has attained its 

 full extension. The aperture of communication in the wall of the 

 globule is but rarely (A . giganteus) visible under the microscope 

 as a fine capillary channel (Fig. 163, c). The secondary sterig- 

 mata, first observed by Berkeley (in 1857) and Cramer (in 1860), 

 are formed in succession from their parent cell. 



Malformations are by no means rare in many species (A. 

 glancus, A. oryzce, A.Jlavus, A. niger, A. ochraceus, A.fumigatus, 

 Ac.), and have often been described. They include outgrowth of 

 sterigmata into elongated tubes, vegetative hyphre, and even 

 into dwarf conidiophores ; globular swellings of the vegetative 

 hyphre ; irregular branching of the conidiophore apex, the globules 

 being no longer formed ; forking of the stem ; abnormal branching 

 of otherwise simple sterigmata, &c. It is sufficient here to merely 

 record such (really unimportant) facts in order that they may be 

 appreciated at their true value when observed. The occurrence 

 of septa in the stem (especially in A. flavus), and sterigmata 

 should probably be placed in the same category; at least this, 

 and the often observed branching of the conidiophores, seem to 

 be merely sports and not constant characteristics, the conidio- 

 phore, as a rule, consisting of an unbranched, unicellular hypha. 



It is also worthy of notice that many species nourish best at a 

 high temperature (about 35-4o C.), e.g., A. flavins, A. niger, A. 

 onjzce, A. clavatus, A. fumigatus, A. nidulans, A. Wentii, a fact 

 which may be utilised in the rapid differentiation of species. 

 Among the kinds known at present, only A. glaucus and A. 

 candidus exhibit a preference for low temperatures, though even 

 many of the heat-loving species will pull through at very low 

 temperatures (A. niger and A. oryzce will grow below ioC.). 



A summary of the species may now be given, this being confined 

 to the better known or more fully described (newer) kinds, 

 omitting the numerous older and often unrecognisable ones. 

 Those of technical importance are indicated by thicker type. It 

 should be noted that the colour of the vegetation is not invariable, 

 being influenced by the substratum, some green or white species, 

 for example, occasionally becoming yellow, whilst, according to 

 Vuillemin, the colour of A. versicolor ranges from green to red. 

 The species in group 4 undoubtedly include several synonyms, 

 and also the white (2) and blackish brown (3) kinds require eluci- 

 dation, so that in reality only the green species can be regarded as 

 anything like properly established. 



