VEGETABLE CYTOLOGY 
41 
Chromoplastids are plastids found in cells independent of their 
relation to light or darkness and contain a yellow, orange or red 
pigment called chromophyll. 
Fig. 13. — A, embryonic cells from onion root tip; d, plasmatic membrane; c, cy- 
toplasm; a, nuclear membrane enclosing the thread-like nuclear reticulum; b, 
nucleolus; e , plastids (black dots scattered about). B, older cells farther back 
from the root tip. The cytoplasm is becoming vacuolate; /, vacuole. C, a cell 
from the epidermis of the mid-rib of Tradescantia zebrina, in its natural condi- 
tion on the right, and plasmolyzed by a salt solution on the left; g, space left by 
the recedence of the cytoplasm from the wall; the plasma membrane can now be 
seen as a delicate membrane bounding the shrunken protoplast. All highly mag- 
nified. (Stevens.) 
CELL FORMATION AND REPRODUCTION 
The cells of plants have all been derived from preexisting cells. 
In the bacteria and many other low forms of plant life, the division 
of the cell always results in reproduction; in higher forms, however, 
it merely increases the size of the individual and so is a phenomenon 
of growth. 
( 
