2 BOTANY. 



their growth ; 2, watery 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, Avhich facilitates the reception 

 of nutriment, operates in respiration and in the coloration of the dififerent 

 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 likcAvise 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. Cellular 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 

 o-eneral. 2. Sphccrencliyma, spherical cells. 3. Merenchyma, spheroidal 

 cells. 4. Ovenchyma, oval cells, — very common in herbaceous plants. 5. 

 Co7ienchyma, conical cells, as in some hairs. 6. Columnar tissue, divided 

 into Cylinclrenchyma, where the cells are cylindrical, and Prismenchyma. 

 where they are prismatic. This, wdien compressed, becomes M^iriform, 

 and when depressed, PineTichyma. 7. Prosenchyma, fusiform, or spindle- 

 shaped cells, as in bark and wood. 8. Colpeachyma, sinuous or waved 

 cells. 9. Cladenchyma, jjranched cells, as in some hairs. 10. Actinenchyrna. 

 stellate or radiating cells. 11. Doedalenchyma, 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 3V of an inch in 

 diameter ; the more usual size, however, is j^^, sometimes ^^V^- Each cell 

 is originally isolated with a completely investing wall, Avhich, 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 



