304 
W. B. Mercer, 
The amount of modification which the extruded spores undergo 
varies with different media. On all the agar preparations used the changes 
were fairly uniform, but on gelatine media the alteration was confined to 
swelling of a limited number, with browning in a few instances. 
On most other solid media e. g. Carrot, Radish etc., as also in liquid 
hanging drops the amount of change was similar to that on agar; on 
potato, however, and to a lesser degree on Asparagus a very large pro¬ 
portion of the spores swelled and divided forming dark masses, tissue¬ 
like in section. 
On all media a few of the extruded spores germinated normally, 
but the growth of the resulting plants was usually limited and not infre¬ 
quently abnormal; e. g. Fig. 6 , 1—4 on Casein gelatine; frequently, too, 
gemmae were formed from the spore after germination. 
The close resemblance between the alterations undergone in the 
normal course of events, when spores are extruded on to the food medium 
and those taking place in fresh spores in crowded hanging drops justifies 
the belief that the same factors are involved in each case, the changes 
being slower and less general in the former instance owing, probably, to 
lack of moisture. To make sure of this a piece of agar was cut out of 
an old PETRi-dish culture, and covered with water in a sterile dish. A 
great number of spores floated to the surface, on which a skin quickly 
formed; there was soon a great development of the characteristic growths. 
Those remaining below the surface of the water, like those suspended in 
the hanging drops of sugar solution, underwent little change. 
In following the morphology of this fungus interesting physiological 
questions are raised, in particular that of poisonous excretions. It is 
known that many bacteria excrete substances inhibitory to their own 
growth, e. g. Psetodomonas destructans 1 ). Wehmer 2 ) has shown that 
Pénicillium italicum and Pénicillium olivaceum similarly poison their 
own food medium by excreted waste products. The behaviour of the 
present fungus is at times very suggestive of the results of a self-poisoning 
action. The concentration of the protoplasm of the mycelium in short 
stretches, the formation of thick-walled brown conidia and gemmae are 
apparent indications of an adaptation to unfavourable circumstances; while 
the fact that these growths only occur late in life 3 ) is suggestive of a 
disturbance of physiological, not purely physical, balance. 
The darkening of the agar in a culture can be due to only one of 
two causes; either to some substance excreted from the fungus, or to 
purely chemical changes going on in the agar as a result of the absorption 
of some of its ingredients. In either case the effect would be cumulative. 
So, too, the formation of an especially dark halo around the gemmae 
could be explained on either ground, for as the dark patches are formed 
around parts of the plant in which protoplasm is massed (as opposed to 
the greater part of the mycelium, which loses its contents after a time) it 
is natural that the changes in the agar should be most marked in these 
regions. The variation in the amount of discolouration in different media 
1 ) Potter, Journ. Agric. Sc. 1908 , Vol. IN, Part I, p. 103 . 
2) Wehmer, Beiträge zur Kenntnis einheimischer Pilze II, 1895 . 
3 ) A PETRi-dish is overspread by the mycelium in about a week, but the 
brown conidia and gemmae appear chiefly after the culture is a month old. 
