82 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 
shown, in which ordinary plants, as Cress, have been induced to become 
fleshy by watering them with a solution of salt. Still the question arises,. 
How can such variations in plant- structure come about ? 
We have seen how the nucleus by division produces two cells out of 
one. Secondly, we know that the cells grow into definite shapes accord- 
ing to their positions and requirements in the plant. Thirdly, we know 
that groups of such cells of various kinds form plant-organs, as roots,, 
leaves, bracts, sepals, petals, &c. Now, when we examine such variations 
as mentioned in the Common Knotgrass, we see the ultimate result of the 
effect of the different soils upon the seeds growing up in them ; in that 
variations of structure appear from some one, assumed as the type form.. 
We know, therefore, that the cells must have been grouped differently 
from their arrangements in the typical plant, and they thus again are 
due to the behaviour of the nucleus and protoplasm. 
Hence there is no alternative to the statement that we must look to 
the protoplasm and nucleus as the responsive agents, which set to 
work to build up cells, &c. ; so that the altered organs may be better 
suited to the new conditions under which the plant finds itself. 
This is why many botanists have noted the fact when exploring 
countries, that to look for varieties of any species, they are always more 
generally to be found on the confines of the geographical area, in which 
the plant has its special habitat ; simply because the further afield it 
travels the greater will be the chances of the external conditions being 
different. 
That it is simply the environment which brings about adaptive 
features in plants, is seen from the fact that many of the plants of any 
area of a marked climatal character put on almost identically the same 
forms, though they may have no affinity between them whatever. Such 
is particularly observable in the inhabitants of such environments as, 
very dry and barren soils, as of deserts. On the other hand aquatic; 
plants show marked peculiarities of adaptation to a watery medium,, 
which can only be the result of the action of the water conjointly with 
the adaptability of the protoplasm in the submerged plant. 
As examples of desert plants there are two well marked features : 
one is spinescence, if the plant be woody ; and the other is succulency, if 
it be herbaceous. In the deserts around Cairo one of the largest bushes 
(2 ft. to 3 ft.) is a member of the Cruciferce, having stiff spines ; but other 
plants might be mentioned as having spiny leaves, such as Cornulaca,. 
Sal sola, &c. 
In our own country spinescence is seen in Gorse, the Needle-furze,. 
Juniper, and Rest Harrow, &c., all growing in a poor soil. 
As examples of succulent plants there are the cactaceous plants of 
Mexico, the .Euphorbias and the Stapelias of Africa. 
Our Sedums, Houseleek, and Cotyledon umhilicus are examples. 
The conclusion is inevitable that by growing under similar climatal 
conditions, and rocky, barren soils, having to endure long and intense 
droughts, plants have gradually acquired precisely similar structures, 
because they are the best suited for them under the circumstances. Pro- 
toplasm, being the same in all plants, has, therefore, built up similar 
tissues and like organs in the above named plants, although there is nov 
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