Brooks . — - Observations on the Biology of Botrytis cinerea . 485 
of the starved leaves is earlier than the time when such a truly saprophytic 
mould as Penicillium begins to flourish upon them. This is in accordance 
with the view which considers Botrytis to be a hemi-saprophyte. Its mode 
of nutrition cannot be placed in the same category of saprophytism with 
that of such a fungus as Penicillium or Eurotium ; nor can it be considered 
a true parasite, for it kills tissues in advance of its own growth. 
While the experiments already described were being carried on, 
another series was in progress, in which the Lettuce plants were grown 
under different conditions of mineral starvation. It was desired to ascertain 
whether plants, grown in a substratum which was deprived of certain 
mineral supplies, were more liable to infection by Botrytis conidia than 
plants grown in ordinary soil. Lettuce seeds were sown in fine sand, 
chemically pure, placed in circular glass jars. At the bottom of each jar 
a small inverted flower-pot had been placed in an inverted position, and 
passing through the hole in the flower-pot was a glass tube, as will be seen 
in the accompanying sketch. Some pieces of broken glass put around the 
flower-pot served to prevent the sand from falling and filling the air space 
within the flower-pot. Each day during the progress of the cultures the 
air was sucked up from the bottom of the jars by means of the glass tube. 
In this way the proper aeration of the roots was provided for. The pre- 
caution was taken of sterilizing each part of the apparatus separately, and 
each jar when fully set up was sterilized again prior to the sowing of the 
seeds. Black paper was bound round the outside of the jars in order 
to prevent the growth of Algae within. 
The culture solutions chosen were those devoid of potassium, mag- 
nesium, nitrogen, and phosphorus, respectively, and of course there was 
a control experiment in which the solution used contained all the normal 
mineral ingredients. All the solutions were made up according to the 
formulae given on p. 224 of Macdougal’s Textbook of Physiology. After 
the seeds had been sown the cultures were moistened with distilled water 
until the cotyledons appeared. Then the young plants were watered every 
other day for a fortnight with the culture solutions, after which they were 
treated in the same way every third day. On other days the sand was 
moistened with distilled water, if this was thought necessary. Care was 
taken to avoid any collection of liquid at the bottom of the jars, so there 
was no danger of the roots being water-logged. The cultures were placed 
under large bell-jars in a greenhouse, the temperature of which varied 
between io° and 20° C. The plants grew well under the conditions of the 
experiment. Six weeks after sowing the seed each plant grown in the jar 
containing the normal mineral supplies, and in those devoid of nitrogen 
and magnesium respectively, possessed 4-5 ordinary foliage leaves, the 
largest being 1-5 c.m. in diameter. The plants grown in sand devoid of 
phosphorus were about half the size of those just mentioned, while those 
