OIDIUM ALBICANS. 195 



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apt to appear, by their peculiar mode of occurrence, for the most 



part, in groups of two. Both spores and filaments resist even 

 concentrated sulphuric and nitric acid. The fresh fungi are 

 shorter, not ramified, the partition walls are closer together, 

 the contractions rarer, the filaments more regularly cylindrical, 

 and the contents of the terminal cells of the filaments paler. The 

 same may be observed in algae which have been kept in water for 

 several days. Reubold observes that, on the whole, little is to be 

 added to this description as given by Robin. He also speaks of 

 the spores and of the partition walls and the contractions, rarely 

 found on any fungus of the skin, as well as of the oval violet- 

 coloured cavities, as highly characteristic of this fungus, 

 although they are sometimes small in number. Reubold 

 deviates from Robin merely in assuming the existence of two 

 kinds of germination in the spores. 



Threads of various thickness, with partition walls and 

 contractions whence the branches arise, spring from the ends or 

 sides of the spores, whilst in their interior granules and mole- 

 cules are found. The filaments betoken their origin, according 

 to the position of the spores, sometimes as shining points, some- 

 times as projections. Very thin threads frequently originate 

 during the germination, which are often of considerable length, 

 and without any partition walls or contractions, exhibiting only 

 numerous dense cavities, which, however, finally expand. Robin 

 does not seem to be aware of this kind of development, whilst he 

 knew well the second kind, where the fungus is developed by 

 mere prolongation of the spore, and direct transformation into 

 threads. The spore becomes longer during this process; the 

 cavity remains the same, whilst the prolongation may give rise to 

 a new cavity, or frequently to two, three, or four, side by side, 

 beginning as small points. These spaces enlarge as the cell en- 

 larges and elongates ; they touch one another, and finally leave 

 only small partition walls between them, so as to transform these 

 partitions riot into new formations, as Robin states, but into the 

 remains of a previous solidity. The same formation of expanding 

 hollow spaces occurs during germination j the two kinds of de- 

 velopment are sometimes met with during the same germination. 

 The ramifications, which have the same diameter as the principal 

 trunks, are for the most part only perceptible in the first order ; 

 ramifications of the second, third, and fourth order are, however, 

 often found. Very neat dendritical figures occasionally occur. 



