510 Armstrong . — The Function of Hormones in 
plants was omitted from the communication we may be allowed to repro- 
duce it verbally as presented to the Royal Society : — 
‘It is the common practice among gardeners in the afternoon, after 
watering the plants in a glass house, to spray the leaves more or less heavily 
with water and then to close the house. During the daytime, while 
regenerative changes prevail, the proportion of diffusible hormones in cir- 
culation must be relatively small and water will have little tendency to 
pass in through the leaf surfaces ; as the light diminishes, degenerative 
changes set in and gradually increase in intensity — these undoubtedly give 
rise to carbon dioxide and other hormones which serve to induce the entry 
of water at the leaf surface. The development of perfume by flowering 
plants, &c., in the evening, is clearly an external manifestation of the 
beginning of the degradation process ; flowering, in fact, marks the onset of 
the period when degenerative processes begin to prevail and the accumu- 
lated stores of material are set in circulation to develop the reproductive 
organs and seed. The perfume itself must exercise a stimulative influence 
on the plant in which it is produced. 
‘Attention has been directed to the effects produced by sterilizing soils 
more or less completely through recent work done in the Rothamsted 
laboratory by Russell and others. Partially sterilized soils are more rapidly 
oxidizable than unsterilized and the fertility of a soil is greatly increased 
by partial sterilization. These results are attributed with reason to the 
destruction of protozoa, which normally fatten on the Bacteria and prevent 
these latter from determining the gradual break-down of organic matters in 
the soil into the materials which serve as plant food. The nitrifying Bac- 
teria are killed off but other Bacteria survive and these tend to produce 
ammonia among other things — so that partially sterilized soils are rich 
both in carbon dioxide and ammonia in comparison with the unsterilized. 
We are inclined to believe that these two factors are of prime importance 
in facilitating plant growth by affording the stimuli required to determine 
the degenerative changes involved in the translocation of nutritive materials. 
‘ Mr. Pickering has shown that, in soils which have been more or less 
effectually sterilized by heating, the germination of seeds takes place much 
less rapidly than in unsterilized soils, if at all. He attributes this result to the 
production of a substance or substances which have a directly toxic effect. 
We are inclined to think that in such soils the necessary stimulus to the 
inhibition of water and germination is lacking, chiefly because carbon 
dioxide and ammonia— the latter especially, perhaps — are produced only in 
abnormally small amounts, if at all. We doubt if seeds would germinate in 
pure sterile water . 1 
1 It is well known that it is difficult to sterilize the exterior of seeds. Our observations show 
that ordinary sterilizing agents should not be used, as these will penetrate into the seed. Taking 
into account Adrian J. Brown’s observations, it is clear that one of the best ways to sterilize cereal 
