85 
tion indicate their growth and powers of continu- 
ance : they have no capability of distinguishing be- 
tween the hurtful and the wholesome ; and if un- 
provided with a supply of materials for imbibition 
and absorption, they must perish. As nothing but 
matter so delicate as to pass through perforatione, 
which the human senses, aided by the most power- 
ful microscopes cannot distinguish, is fitted for the 
support of plants; and no inorganic matter, but 
water or air, or substances held in solution by the 
two fluids the aériform and the aqueous can answer 
this description, air and water become the essential 
elements for the support of vegetable life. 
When we advance from the living bodies which 
we recognise as absolutely vegetable, to those which 
we perceive to be absolutely animal, by the interme- 
diate links that unite both, we find a difficulty in 
applying the distinctions we have just insigted upon 
to the higher endowments in the lower ranges of 
organic life, and to the lower endowments in the 
higher. We find that the character we have as- 
signed, will not apply with exactness to either the 
animal or the vegetable kingdom. Let us take up 
the genera Diaioma or /ragillaria, and set these by 
the side of some tribe of aggregated Ascidians such 
for instance as the Botryllus, ‘The individuals of 
this tribe which at acertaia period of their existence 
unite to form one common mass or system, float se- 
parate and free at first; and the disjointed aloz, 
diatoma and fragillaria, living in society and dis- 
persing to multiply, shake cur confidence in sponta- 
neous motion from place to place as a test of animal 
3 
