_ called the nutrient substances of the plant. 
s , Ben 4s tructurad and Ph iysilogioa! Botany. 
eaboemces then. cease fp exercise theit chemical influence on ; 
one another. If the plant is not to perish from the deficiency cae 
thus occasioned of formative materials and of sources of force, 2 
or, as it were, to be starved, it must be supplied with nutrient —, — 
substances, z.e. with chemical compounds which contain the 
substances that it requires. Only in comparatively few cases ~ 
is a chemical compound absorbed into the plant which will 
be useful to it without change ; as arule, itis only the separate ~ 
elements which are indispensable, and are on that account ~~ 
taken up out of their compounds. Those elements which | 
are indispensable for the entire processes of vegetation are é 
. If we pass in review the elements which play this part 
in the vegetable kingdom, we find that the list comprises - 
carbon, oxysen, nitrogen, hydrogen, and sulphur, because these 
enter into the composition of protoplasm, and are conse- a 
quently necessary for the formation of every vegetable cell. 
To them must also be added cron, calcium, potassium, magne- 
sium, and phosphorus, because no instance is at present 
known of a plant retaining its normal state of health if de- — 
prived of any one of these elements. Sod¢um and chlorine 
must also probably be included. In addition to these uni- 
versally distributed nutrient materials, the growth of some 
plants is also dependent on the presence of other special 
elements ; although we have no exact knowledge of the 
part which they play, and are unable to state positively that a 
they are indispensable. ‘Thus Viola calaminaria and some ~ 
other plants always contain zinc, and will only grow on~- 
soil which contains that element. 
The organ by means of which the nutrient substances 
are taken up is, in the lower plants, the entire surface ; in 
the higher plants this function is specially assigned to 
the root, which is constructed for this purpose. In 
the case of roots which penetrate into the soil, only the 
youngest parts, with their delicate root-hairs and papilla, 
can perform this function ; but in the aerial roots of some. 
