320 
Notes. 
These experiments prove what has previously only been assumed, namely, that 
parasitism in Fungi is an acquired habit. 
A series of experiments prove that infection of plants by Fungi occurs more 
especially during the night, or in dull, damp weather. This is due to the greater 
turgidity of the cells, and also to the presence of a larger amount of sugar and other 
chemotactic substances present in the cell-sap under those conditions. 
GEORGE MASSES, Kew. 
CULTURAL EXPERIMENTS WITH ‘ BIOLOGIC FORMS’ OF THE 
ERYSIPHACEAE k — In the introductory remarks the author points out that through 
specialization of parasitism 4 biologic forms ’ have been evolved in the Erysiphaceae 
which, both in their conidial (asexual) stage and ascigerous (sexual) stage, show 
specialized and restricted powers of infection. The powers of infection, characteristic 
of each 4 biologic form,’ are under normal conditions sharply defined and fixed, and 
hitherto the result of the experiments of numerous investigators — both in regard to the 
present group of Fungi and to the Uredineae, where the same specialization of parasitism 
occurs — has been the accumulation of evidence tending to emphasize the immutability 
of £ biologic forms/ 
The second part of the paper gives the result of cultural experiments with 
‘ biologic forms ’ of Erysiphe Graminis DC., carried out during the past summer in 
the Cambridge University Botanical Laboratory. It has been found that under 
certain methods of culture, in which the vitality of the host-leaf is interfered with, the 
restricted powers of infection, characteristic of ‘ biologic forms,' break down. 
In the first method of culture adopted, the leaf, which was either attached to 
a growing plant, or removed and placed in a damp chamber, was injured by the 
removal of a minute piece of leaf-tissue. In this operation the epidermal cells on one 
surface, and all or most of the mesophyll tissue, were removed at the cut place, but the 
epidermal cells on the other surface (opposite the cut) were left uninjured. Conidia 
were sown on the cuticular surface of the uninjured epidermal cells over the cut. In 
a few experiments the conidia were sown on the internal tissues of the leaf exposed by 
the cut, and these gave the same results. 
Using this method of culture, over fifty successful experiments, of which details 
are given, were made. In these the conidia of certain ‘ biologic forms ’ were induced 
to infect ‘ cut ’ leaves of host-species which are normally immune against their attacks. 
The experiments proved that the range of infection of a ‘ biologic form ' becomes 
increased when the vitality of a leaf is affected by injury, and also that species of 
plants ‘ immune ' in nature can be artificially rendered susceptible. 
Further experiments showed that the conidia of the Fungus produced on a ‘ cut ' leaf 
are able at once to infect fully wiinjured leaves of the same host-species. 
In other experiments, a method suggested by Professor H. Marshall Ward with 
the object of avoiding lesion of the leaf, was adopted. Leaves were injured by 
touching the upper epidermis for a few seconds with a red-hot knife, and conidia were 
1 Abstract, reprinted from the Proceedings of the Royal Society. 
[Annals of Botany, Vol. XVIII. No. LXX. April, 1904.] 
