Brenchley . — The Development of the Gram of Barley. 921 
ceased, material is still transferred to the grain at the expense of the straw. 
It seems that in the case of barley the limiting of one factor of the food 
supply limits the availability of other food substances, i. e. that in the 
absence of a sufficiency of one essential food the plant is unable to utilize 
others even in the midst of plenty. 
The effect of P 2 O s -starvation is the more intensified with the barley 
from plot C, since the plant is supplied with an excess of potash and other 
alkalis in addition to nitrogen, the only shortage being in the phosphoric 
acid, whereas in the compared wheat plot a general deficiency existed 
in everything except nitrogen (of which an excess was present), so that the 
particular effect of lack of phosphoric acid was not so marked. 
The difference in the effect of P 2 0 5 starvation on barley and wheat 
is also partly due to the diversity in the root systems. Barley, being 
shallow rooted, rapidly exhausts the supply of a plant food of which a 
storage exists in the surface soil. Wheat, being deep rooted, is able to seek 
its food from a much greater area of soil in the underlying strata, and conse- 
quently in a soil continuously cropped and P 2 0 5 -starved it is probable that 
such a sufficiency of phosphoric acid is available that the limiting factor does 
not come into play, and so far as the wheat is concerned phosphoric acid 
starvation does not exist in the plot considered. 
B. Points of Biological Interest. 
Preparation of material. While the mature barley grain is of a composite 
nature, consisting of the fruit and the palea and glume welded inseparably 
together, the young developing grain can be easily separated into its consti- 
tuent parts, as the union is a later feature in development. For about 
fifteen days from the time of flowering, fruit and glumes are distinct individuals, 
and they can be detached without injury to either member ; the actual 
junction appears to occur fairly rapidly, within a very few days. 
The existence of the semi-permeable membrane 1 is a source of difficulty 
with regard to the penetration of reagents. At least three days before the 
glumes begin to unite with the grain, this layer is evidently in full activity, 
as experiments indicated. Grains were taken fresh from the plant, placed 
for one day in 3 per cent. AgNO a , then one day in 5 per cent. NaCl. 
Examination showed that the reagents penetrated the glumes freely, but 
failed to gain access to the endosperm, which „ remained quite colourless. 
The outer coats of the grain were a little darkened just under the glumes, 
showing that the AgN 0 3 had probably succeeded in penetrating a short 
distance into the seed coats. In view of this difficulty in penetration, after 
the first ten days from flowering most of the grains selected for pickling 
were slightly pricked, so as to secure efficient killing and fixing of the 
material. The reagents used were acetic alcohol, with an immersion of 
1 Brown, A. J. : Ann. Bot., Ixxxi, 1907, pp. 79-87. 
