49 . BOTANY. 
roots. and circulated along with the sap; these consist mainly of air, oxygen, 
and carbonic acid. In the course of the ascent slight changes take place 
in the sap, the most important, however, being reserved for the leaves to 
effect. Here the sap is exposed to the influence of light and air, by means 
of which carbon and hydrogen are fixed, oxygen and watery vapor given off. 
The sap thus becomes denser and more fitted to the purposes for which it is 
destined. After this elaboration it commences its descent, passing through 
the bark, and transmitted laterally through the cells of the medullary rays. 
The descending sap, or Jater, is sometimes clear and transparent, at other 
times it is milky or otherwise colored. In this are contained the peculiar pro- 
ducts of the plant which are deposited in various situations. A mucilaginous 
deposit between the bark and the wood results in the formation of an external 
layer to the latter, and an internal to the former. Starch and gum are depos- 
ited in the cells of the new layer of alburnum or sap wood, which, in the spring 
of the year, may be converted into sugar, and by solution in the ascending sap 
impart to this its sweetness. 
ON THE GEOGRAPHY OF PLANTS. 
Plants are found distributed all over the surface of the earth, wherever 
heat, air, and moisture co-exist; and the warmer and moister the country, 
the more vigorous and varied the vegetation.. The same soil, however, is 
not equally favorable to all plants; this is mainly owing to the fact, that 
different species require different organic ingredients, as well as different 
amounts of heat, light, and moisture. The mean temperature of a place 
exerts great influence upon its vegetation, and as this temperature is 
affected to a certain extent by the latitude and longitude, it becomes possible 
to establish an intimate relation between geographical localities and 
particular forms of plants. Besides the geographical arrangement of plants, 
we may also have a physical grouping, according to the physical features 
of the soil in which they are found. Thus plants may grow in water, salt 
or fresh, they may be found in sandy soils, in meadows, in vegetable mould, 
under trees, or on other plants, and even on animals. Recent discoveries 
of the highest interest, by Dr. Leidy of Philadelphia, have shown that the 
occurrence of entophyta in animals is perfectly normal. The following 
arrangement by Balfour, exhibits the general features of a division of plants, 
according to their station. 
A. Prants Growine In WATER, WHETHER Sat or FREsH. 
» 1. Marine Plants, such as sea-weeds, Lavers, &c., which are either buried 
in the ocean or float on its surface ; also, such plants as Ruppia and Zostera. 
In the Sargasso Sea there are floating meadows of Sargassum bacciferum— 
gulf-weed. This sea extends from 22° to 36° north latitude, and from 25° 
42 
