A LINEAR AGGREGATE 185 



D, more advanced mycelium : the hypha; have increased in length 

 and begun to branch, and septa (sep) have appeared. 



E, germinating spore (sp) very highly magnified, sending out one 

 short and one long hypha, the latter with a short lateral branch and 

 several septa (sep). Both spore and hyphae contain vacuoles (vac] in 

 their protoplasm. 



F^F 4 , development of the spore-bearing brushes by repeated branch- 

 ing of an aerial hypha : the short terminal branches or sterigmata are 

 already being constricted to form spores. 



F 5 , a fully-developed brush with a row of spores developed from each 

 sterigma (stg). 



F 6 , a single sterigma (stg) with its spores (sp). 



F 7 , an over-ripe brush in which the structure is obscured by spores 

 which have dropped from the sterigmata. 



B-D, F^F 5 , and F 7 X 150 : F 6 X 200 : E X 500. 



As long as the growths are white or blue in colour no 

 powder can be detached by touching the aerial hyphae, 

 showing that the spores are not yet fully formed, but as soon 

 as the permanent green hue is attained the slightest touch 

 is sufficient to detach large quantities of spores. 



A bit of the felt-like mycelium is easily teased out or torn 

 asunder with two needles, and is then found, like actual felt, 

 to be formed of a close interlacement of delicate threads (D). 

 These are the mycelial hyp/ice : they are regularly cylindrical, 

 about T jQ- mm. in diameter, frequently branched, and differ 

 in an important particular from the somewhat similar hyphae 

 of Mucor (p. 159). The protoplasm is not continuous, but is 

 interrupted at regular intervals by transverse partitions or 

 septa (D, E, sep). In other words, a hypha of Penicillium 

 is normally, what a hypha of Mucor becomes under un- 

 favourable conditions (p. 160), multicellular^ the septa dividing 

 it into separate portions, each of which is morphologically 

 comparable to a single yeast-cell. 



Penicillium shows therefore a very important advance in 

 structure over the organisms hitherto considered. While in 

 these latter the entire organism is a single cell ; in Peni- 



