150 
JOUB>'AL OF THE ROYAL HOETICULTURAL SOCIETY. 
lion or probably precipitation subsequent to the entry into the vessels, 
the details of which operation escape us. Soda is always met with in 
plants, and may be derived from the decomposition of the felspath albite. 
In marine climates chloride of sodium is found in abundance, and it is 
estimated, for instance, that on the plain of Caen the contribution of 
marine sahs by the rain water is not less than 50 kilos, per hectare per 
annum. 
Alumina. — The existence of alumina in plants has been the subject 
of numerous discussions. M. Berthelot has been able to show that 
alumina exists in the ashes of annual plants with abundant roots. The 
alumina appears to become fixed in the tissues in the form of phosphate 
of alumina, and does not seem to pass beyond the stalks. 
Manganese, zinc, and copper have been observed in vegetable tissues. 
I have myself found measm-able quantities of manganese in Orchids 
of the genus Cattleya. and in the petals of Roses ; but we have no indica- 
tion of their ntility, nor of their mode of entry into the plants. 
Chemical analysis, such as can nowadays be made, affords us very precise 
and exact information regarding the total number of elements useful to 
plants contained in the soil. With the exception of nitn^en, of which 
we can study the nitrification, and perhaps of phosphoric acid and Ume, 
of which the assimilable quantities may be determined by analysis only, 
we cannot form an idea of the actual condition of assindlability of tiie 
elements useful to plants, but, on the other hand, we can clearly deter- 
mine whether the total quantity of each of the contained elements is 
insufiicient. and so be enabled to assure cultural success by providing 
compleinentaiy manures. It suffices for that purpose to take the thick- 
ness of the cultivable soil, then the density of same, and finally multiply 
the weight of the arable deposit by the figures expressing the composition 
of the kilo, of soil in a fresh condition ; the result then at once 
appears. 
The greatest help to progress that agronomic science has given to 
modem horticulture is the determination of the composition of crops, 
permitting thereby the composition of the soil being known, and the cal- 
culation and restitution of ail the elements withdrawn by them. Such a 
restitution is indispensable in order to secure the maintenance of present 
fertihty and the success of future cultivation. 
