32 
lately brought into notice by Dr. Richardson, more 
food may, however, be produced upon an irregu- 
lar surface ; but the principle seems to apply 
strictly to corn crops. 
The direction of the radicles and germens is 
such, that both are supplied with food, and acted 
upon by those external agents which are necessary 
for their developement and growth. The roots 
come in contact with the fluids in the ground ; 
the leaves are exposed to light and air ; and the 
same grand law which preserves the planets in 
their orbits, is thus essential to the functions of 
vegetable life. 
When two pieces of polished glass are pressed 
together they adhere to each other, and it requires 
some force to separate them. This is said to 
depend upon the attraction of cohesion. The same 
attraction gives the globular form to drops of 
water, and enables fluids to rise in capillary tubes ; 
and hence it is sometimes called capillary attraction. 
This attraction, like gravitation, seems common to 
all matter, and may be a modification of the same 
general force ; like gravitation, it is of great im- 
portance in vegetation. It preserves the forms of 
aggregation of the parts of plants, and it seems to 
be a principal cause of the absorption of fluids by 
their roots. 
If some pure magnesia, the calcined magnesia 
of druggists, be thrown into distilled vinegar, it 
gradually dissolves. This is said to be owing to 
chemical attraction , the power by which different 
species of matter tend to unite into one com- 
pound. Various kinds of matter unite with dif- 
