PHYSIOLOOY:. 259 
Besides oxygen, ammonia too favdurs the ger- 
mination of seeds; hence seeds germinate almost 
immediately when placed in dung, Ww vhich therefore 
serves as manure. . Cow-dung, we know, consists of 
muriatic acid and ammonia. In fluids which con- 
tain no oxygen, seeds will not germinate. [t never 
happens in oil, for instance, meh consists of hy- 
drogen and carbon. | 
§ 252, 
It is the rostel of seeds which eae jee part 
of a plant under ground, to which botanists have 
given the general name of root, (§ 10). But ese 
ologists call that part only a root, which carries 
nourishment from the soil to the plant, or what we 
before called radicles or fibres, (radicula). 
In under-shrubs this part under ground consists 
of a bulbous, tuberous, or oblong root. In annual 
plants it is more or less perpendicular; and jn shrubs 
and trees its formation entirely resembles the stem. 
In this, foresters again distinguish two separate parts, 
the thick one, which descends perpendicularly, call. 
ed the main root; and those parts which run forth 
horizontally in the earth, which are their horizonial 
roots. 
§ 253. 
The anatomy shows us, that in biennial herbs 
and plants the adducent. and pneumatic vessels 
form a circle or ring in the root, the inside 
of which is filled with pith, the outside lined with 
cellular texture. The reducent vessels lie in the 
aR? last 3 
