172 
NATURE NOTES. 
Here, again, heredity comes into play, for ordinary leaves of 
plants and trees have stomata chiefly or only on the lower and 
not the upper side. Hence the fact that the water Crowfoot 
has them on the upper and not the lower is clearly an adapta- 
tion to their floating on water, because the latter element pre- 
vents their formation on the lower side. 
If the aerial plant be now transformed back again to water 
and submerged, all the “ aerial ” leaves perish, but it throws out 
fresh “ aquatic ” leaves instead. Hence one cannot avoid the 
conclusion that in some way or other an aquatic medium is 
the direct cause of one set of structures, and the aerial that of 
another set. Of course it is not only the difference between 
water and air, but all the concomitant circumstances associated 
with these two media respectively, which make up the environ- 
ment and take effect upon plants. Thus the greater amount of 
light in air than in water acts most powerfully in regulating 
the structure of the tissues ; the difference in the amount of 
carbonic acid, &c., all, no doubt, assert their influence; so that 
the different effects produced in plants are the result of the 
combination of several phenomena acting together. 
In the continuation of this subject I propose to deal with a 
theoretical origin of Floral Structures. 
George Henslow. 
(To be continued..') 
[We have much pleasure in inserting the foregoing able article from Professor 
Henslow, who is an eminent scientific authority, and a valued supporter from 
its foundation of the Selborne Society, of which he is a \ ice-President. It 
must not, however, be supposed that Nature Notes is in any way committed to 
Evolutionist principles. An article on the other side, written with equal know- 
ledge and a similar absence of the polemical spirit, would be just as willingly in- 
serted in our columns.] 
THE PRESERVATION AND ENJOYMENT OF 
OPEN SPACES. 
N the July number of Nature Notes I gave a short 
account of the functions of the three Societies having 
for their object to promote the preservation and enjoy- 
ment of open spaces — the Commons Preservation 
Society, the Kyrle Society, and the Metropolitan Public Gardens 
Association. The movement took its rise in the necessity of 
securing for public use the beautiful commons which lie on. the 
outskirts of London, but it has taken effect in many directions 
since the formation of the Commons Preservation Society in 
1865. I will briefly indicate the several questions which have 
arisen from time to time. 
And first as to common land. Commons are beset by three 
dangers. The}' may be arbitrarily inclosed by the lord of the manor 
