Brown.—Studies in the Physiology of Parasitism. I. 321 
institute a comparison between the action of the extract obtainable from the 
germinating fungus and that of the fungus itself upon the living tissue, this 
feature was very objectionable, and an effort was therefore made to find 
a substitute. This was found in Turnip extract, which has proved to 
possess many advantages. Besides considerations of cheapness and availa¬ 
bility, it is superior to ‘ Grape Juice 5 in its much slighter plasmolytic effects 
while equalling it in the quantity, and more than equalling it in the quality, 
of fungal material which it furnishes. It also possesses the considerable 
advantages that it is only slightly coloured, and its stock solutions can 
withstand repeated heatings without deterioration, whereas ‘ Grape Juice’ 
suffers a definite loss by precipitation at each sterilization. This turnip 
medium is prepared as strong as possible—that is, the turnips (white) are 
autoclaved without addition of water, and the juice subsequently extracted 
under pressure. The most suitable medium is derivable from solid half- 
grown turnips, that from old vacuolated ones being considerably weaker and 
affording a smaller yield of germinated spore material. 
The germination phenomena need not be described in detail. After 
four hours, commencement of germination can be seen in a small number of 
spores; after eight hours, germination is very general, but is variable in 
amount, the germ tube ranging from a mere papilla to a tube of four spore- 
lengths ; at the end of the period allotted, apart from occasional spores 
which have remained clumped together and which may show various stages 
of arrested development, germination is very generally well advanced. The 
young hyphae, by reason of the comparatively thick rate of sowing adopted, 
are all closely intertwined and their individual appearances can only be 
readily seen by tearing out a small portion of the ‘ weft ’. The average 
length of hypha depends naturally on the strength of the particular turnip 
extract employed, but it may be taken as approximating to 20-40 spore 
lengths. While each spore normally puts out a single germ tube, bipolar 
germination is frequent, in which case the length of each tube is less than in 
the normal case. Side branches of first order are not at all uncommon. 
At the conclusion of the period of germination the plates thus present 
a continuous weft of interlocking hyphae, and the whole film may be 
removed as such, much in the same way as a gelatine film may be removed 
from a photographic plate after immersion in warm water. The fungous 
film offers usually considerable resistance to removal, being firmly attached 
to the plate, a phenomenon which finds its explanation in the very general 
development of incipient attachment organs. This is readily verified micro¬ 
scopically, a large proportion of the hyphae showing at their tips the 
flattened slightly swollen appearance characteristic of the early stages of 
these organs. The formation of these attachment organs is very strongly 
marked in sowings in Turnip extract, more so than for instance in sowings 
in ‘ Grape Juice’, and it is at any rate plausible that the superior quality of 
