416 
the circumstances for the circumstances.” That is, in 
effect, the contention of Rev. George Henslow.* 
The evidence in support of the assertion that spines 
are the direct outcome of the environment, rests upon the 
well-known fact that there are many instances of plants 
losing their spines altogether when grown under different 
circumstances. M. Lothelier found that, by growing Ber- 
beris vulgaris in a moist atmosphere, it bore no spinescent 
leaves ; but in a perfectly arid atmosphere, it bore spines 
only. Intensity of light also favoured their production. 
The elongation of the root is caused by the direct 
effect of the water which lies within its reach, or, in other 
words, “ the well-known responsive power of the apices to 
moisture.” Thus if, for example, the tip of the root of a 
seedling turnip gets into a field drain-pipe, it may grow to 
a length of some yards, of course never producing a turnip. 
The hardening of the mechanical tissues generally, which 
so often results in special spiny processes, is brought about 
by drought and other conditions of the environment. 
That the reduction of leaf surface is the result of drought 
is proved in several ways. The same plant will 
produce much larger leaves in March or April when a 
good supply of water is at hand, but minute leaves in 
June when the supply is deficient. If the same plant 
is grown in the Nile Valley, it ceases to produce the 
smaller summer foliage, and resembles the ordinary 
herbaceous leaves of temperate climates. Salvia lanigera, 
growing in the Delta, has flat leaves eight inches in 
length ; but when in the desert they are only about two- 
and-a-half inches long with the margins enrolled. The 
thickness of the cuticle is greater under sunlight than when 
grown in the shade. The production of wax on the 
7'he Journal of the Linnean Society—Botany, vol. xxx., pp. 218-263.