Lae ew ue OS LAE lt Se” haa | | Sou SOC a ft '; z s 
‘ 7 4: he y. “ 
‘ r y j : be ses Wee le toad abe i BE. 1, 
“4h n i " / " ¢ y ’ > =/ 
tative organs, ane a shortening of the duration of their lives. 
The same is the case with these plants which man has 
transplanted from warmer to colder climates or the reverse, 
or has attempted to acclimatise. In order to understand 
this, it is only necessary to observe the weakly specimens of 
tropical plants in our conservatories, and to compare with 
them drawings made in the primeval forests of their native 
country. In short, it may be assumed that all cultivated 
plants are, to a certain extent, disposed to deviate from 
their ordinary structure ; and it cannot, therefore, be won- 
dered at, that they are especially liable to OBIS and 
- diseases. 
Attention must first be directed to those deviations 
which are caused by atmospheric influences, or by the 
nature of the soil. Light, warmth, and moisture, as well as 
the nature and chemical composition of the soil, are here - 
the active factors ; but as to how these act very little is at 
present known, except what has already been said in the 
section on the general conditions of plant life (see p. 208). 
The changes brought about by these influences affect the 
size and number, the arrangement and shape of the indivi- 
dual organs, in short, the external form of the plant; but 
they also cause an abnormal activity of cells, from which 
results a more or less complete disturbance of metastasis 
and of the processes of life. 
The change in size may be partly due to abortion, partly | 
to an abnormal increase in size of the organs. The abortion 
of the primary axis shows itself, as a rule, only in the form 
of dwarjing, that of larger or smaller branches occurs in its” 
purest ae in the production of sfzmes. Several families 
of plants, such as the Rosacee, are especially distinguished 
by the frequency of branch-spines whenever the species 
grow on sterile ground. Like the branches, the leaves can 
also degenerate into spines. Thus, many species of Ber- 
berideze and Grossularieze develope spines in the place of 
particular leaves ; and these often, as in the gooseberry, 
o me The 3 i if the Plant. Kee 217° 
~ 
