ELEMENTS OF ORGANIC STRUCTURE. 231 
cases, however, the cells of plants are so small as to re 
quire a powerful microscope to distinguish them,—are, in 
fact, no more than 1-1200th to 1-200th of an inch in diam- 
eter; many are vastly smaller, 
Growth.—The growth of a plant is nothing more than 
the agoregate result of the enlargement and multiplication 
of the cells which compose it. In most cases the cells at- 
tain their full size ina short time. The continuous growth 
of plants depends, then, chiefly on the constant and rapid 
formation of new cells. 
Cell-multiplication.—The young and active cell always 
contains a nucleus, (fig. 34, 6.) Such a cell may produce 
anew cell by division. In this process 
the nucleus, from which all cell-growth 
appears to originate, is observed to re- 
solve itself into two parts, then the 
protoplasm, @, begins to contract or in- 
fold across the cell in a line correspond- 
ing with the division of the nucleus, until 
the opposite infolded elges meet—like 
Hig 64. the skin of a sausage where a string is 
tightly tied around it,—thus separating the two nuclei and 
inclosing each within its new cell, which is completed by 
a further external growth of cellulose. : 
of the parent-cell, and before they 
obtain full size become entirely 
ing to the old, forming a tissue. Fig. 35. 
In free cell-formation nuclei are observed to develope 
and by the resorption or death of the parent cell become 
independent of the latter. 
In one-celled plants, like yeast, (fig. 35,) the new cells 
thus formed, bud out from the side ; 
detached from it, or, as in higher ee ye | 
plants, the new cells remain adher- 
in the protoplasm of a parent cell, which enlarge, surround 
themselves with their own protoplasm and cell-membrane, 
