112 BOTANICAL GAZETTE [auG 
of the leaf is composed of parenchyma cells which do not show 
differentiatiation at all into palisade and spongy tissue. While 
cells have the shape of those in typical spongy tissue, the large inte 
cellular air spaces characteristic of most mesophytic leaves are he 
replaced by small ones, giving the whole tissue a much more com 
appearance. Not all of the parenchyma cells contain chloropl 
for there are interspersed cells without them, whose function 
of water-storage, having walls provided with large pits which fa 
the passage of water from one cell to another. 
Aside from acting in the capacity of mechanical tissue, the vase 
system has undergone a, process of degeneration. The ne 
for a functional xylem with its transpiration stream is eliminated 
the fact that there is a complete absence of roots, and also by the fa 
that the water-absorbing organs, the scales, are found over the enti 
exposed surface with the exception of some of the floral o 
There would appear also to be no need for a functional phloem 
all living cells either contain chlorophyll and are exposed to light, 
else are approximate to those containing chlorophyll. 
THE CHLOROPLASTS. 
One of the most interesting features of the leaf is the structur 
behavior of the chloroplasts. These bodies, instead of exhi 
the more or less homogeneous structure observed in most chloropl 
are seen to be composed of masses of smaller chloroplasts, meas 
about 2 long and about a third as wide (fig. 52). While a 
few cells in every cross section of the living leaf contain chloro 
of the usual type, the vast majority of them contain such 
been described above. The little chlorophyll bodies have @ 
if not quite, the minuteness of bacteria, and for convenience 
spoken of as microchloroplasts; the larger bodies, of which they 
to form a part, being distinguished as megachloroplasts. The 
significance of the formation of the microchloroplasts will be 
seen when it is stated that they may not remain in bunches (fs. | 
but can and often do separate from one another till the entire & 
plasm of the cell becomes dotted with them (fig. 53)- Under 
magnification such a cell appears uniformly green throughout. 
€ven enter the vacuoles, where a lively Brownian movement is set 
