403 
lengthening and shortening, extending themselves in long curves 
or loops, or contracting into short lines or into little rings. 
When the leaf-cells are active, the protoplasmic meshes are so 
humerous and so conspicuous that the entire cell seems to be 
crowded with the network, within the threads of which float the 
chromatophores like minute green sponges in a colorless, ever 
quivering jelly. | 
Fig. 7 shows the nucleus and its connection with the. proto- 
_ plasmic filaments. Fig. 8 isa transverse vertical section of a leaf 
to show the chromatophores arranged, as they usually are, near 
the upper and the lower cell-walls, with the loose network of pro- 
toplasmic threads and in the central cell, the nucleus temporarily 
adhering to the cell-wall. The leaf varies in thickness from 50 
inch at the Margin to 7$y near the midrib. 
Even in the oldest cells the chromatophores are seldom in con- 
tact even by their enveloping membranes, and if in a healthy con- 
dition there is always a thin layer of protoplasm enclosing and 
Separating each from all the others, and separating each from its 
@pparent contact with the upper and lower cell-walls. When two 
chromatophores are in apparent contact, careful scrutiny with a 
high magnifying power will.exhibit the black spaces between the 
Peripheral trabecule, or the bright, continuous line which is pre- 
Sent between two chloroplasts in which the act of bipartition is 
nearly completed. ; 
Ageratum conyzoides L. cultivated variety Mexicanum. In the 
mésophyll-cells of this plant the chromatophores have a structure 
Similar to that of the chlorophyll-grains of Astrophyllum sylvati- 
cum, the larger having more conspicuous trabeculz, and the sur- 
rounding membrane, which exists here also is raised to a shorter 
distance above the body of the chromatophore on account of the 
lower elevation of the surface-ridges, or of the network of elevated 
lines between which the depressions or apertures, as I believe 
them to be, are placed. : 
Fig. 6 is a diagram of two chloroplasts from this plant in an 
advanced stage of bipartition, with the central apertures somewhat 
©xaggerated, as also are the surface depressions represented by the 
black dots. Attention is asked to the demonstation of the sur- 
rounding membrane where it extends from one chromatophore to 
