9 BOTANY. 
their growth; 2, water, through which, as a dissolving medium, all the 
substances derived from the soil are introduced into the plant; 3, atmo- 
_ Spheric air, from which the plant absorbs carbonic acid by day, fixing 
its carbon, and exhaling the oxygen ; 4, light, which facilitates the reception 
of nutriment, operates in respiration and in the coloration of the different 
parts of the plant, and in part causes the sleep of plants; 5, heat. 
co-operating with light in the last result, and in causing the inhibition of 
liquid food, and likewise influencing germination and the periodical growth 
_ of plants. Electricity has long been known as influencing the growth of 
plants, but the precise nature and extent of its action are not satisfactorily 
established, although numerous experiments have been made on the subject. 
I. ELEMENTARY ORGANS OF PLANTS. 
1. CetuuLarR Tissue. 
CELLULAR Tissue is the elementary material found in all plants, and in all 
parts of the plant. As the name indicates, it is composed of an aggregation 
of cells of different shapes. The single cell, when isolated, is spherical or 
spheroidal, the shape, however, varying considerably when aggregated. 
Some special names for differently shaped aggregated cells, are as follows ; 
1. Parenchyma, cells of dodecahedral character, and whose transverse 
section is subhexagonal. The term has been applied to cellular tissue in 
general. 2. Spherenchyma, spherical cells. 38. Merenchyma, spheroidal 
cells. 4. Ovenchyma, oval cells,—very common in herbaceous plants. 5. 
Conenchyma, conical cells, as in some hairs. 6. Colwmnar tissue, divided 
into Cylindrenchyma, where the cells are cylindrical, and Prismenchyma, 
where they are prismatic. This, when compressed, becomes Muriform, 
and when depressed, Pinenchyma. T. Prosenchyma, fusiform, or spindle- 
shaped cells, as in bark and wood. 8. Colpenchyma, smuous or waved 
cells. 9. Cladenchyma, branched cells, as in some hairs. 10. Actinenchyma, 
stellate or radiating cells. 11. Dedalenchyma, entangled, branched, and 
tabular cells. 
The size of cells varies greatly, not only in different plants, but in 
different parts of the same plant. The largest are about 5 of an inch in 
diameter ; the more usual size, however, is ;4;, sometimes ;,);;- Hach cell 
is originally isolated with a completely investing wall, which, however, in 
some rare instances, is observed to be perforated. The passage. of liquids 
in and out of the single cell is performed by endosmosis. . The anatomy of 
the cell itself and the probable mode of reproduction will be referred to 
hereafter. Although cells have each a distinct wall, so that when two come 
in contact they are separated by a double partition, yet this, on the one 
hand, may appear to be single, and on the other, may become entirely 
absorbed, so as to form a continuous cavity. There may, at times, be a 
lateral communication between contiguous series of cells. Single cells, such 
2 
