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really hot day must be very considerable. This, again, is obviatea 
by a grassy covering which prevents excessive loss of water although 
the grass itself is transpiring freely. 
GRASS TOXINS. 
Now there comes the question of root toxins, about which we 
may say that as yet really very little is known. We know that in 
the case of herbaceous plants rotation of crops is essential, that 
plants of the same kind cannot be grown successfully on the same 
soil continuously, and we also know that seedlings of a big tree do 
not thrive beneath the shade, or perhaps within the root-area of the 
mother tree, whence nearly all trees climbers and other such plants 
have special modifications of fruit or seed to disperse the seed from 
the parent. These facts are accounted for by the theory that plants 
excrete from their roots a poison or toxin. 
The most important contribution to our knowledge on this sub- 
ject is the paper by F. Fletcher in the memoirs of the department of 
agriculture in India, Vol. II. No. 3, “ note on a toxic substance 
excreted by the roots of plants.” He worked exclusively with her- 
baceous plants, cotton, sorghum, wheat, etc. His experiments tend 
to show that the toxins of different plants are identical, and that 
solutions made of them differed in toxic effect only from their strength 
and not from their kind. 
If then all plants produce through their roots a toxin poisonous 
to other plants, this toxin being the same for all plants it is impos- 
sible to see how a grass plot or forest can exist for more f Han a few 
years. As soon as a forest tree had produced a certain amount of 
toxin everything in the neighbourhood of its roots should die. If 
each plant had its own toxin which was poisonous to its own species 
only, it is not clear how one tree forests, such as the pine forests of 
Europe, or coconut tree estate could exist at all, nor does the sugges- 
tion that in the case of sorghum and cotton grown on the same soil 
the roots of cotton godown below the sorghum root area and the 
toxin is retained by the roots of the sorghum when decaying and thus 
the cotton is not affected after the death of the sorghum. 
In a grassplot and in a forest the roots of the different plants are 
intimately mixed in the same layer of soil, and yet the plants grow 
healthily together and the chief struggle between them seems to be 
for light, and soil food. 
The whole subject is very puzzling and difficult to understand, 
and it is clear that much more research is required to dear up these 
points. 
What is really wanted is some system by which we can, while 
avoiding all injury caused by toxins of grass or other herbs, to pre- 
vent the excessive loss of soil and plant food by denudation, and loss 
of water and root injury by the great heat of the sun striking on the 
bare soil. — E d. 
