350 BOTANICAL GAZETTE [MAY 
MENDELIAN WHITE STRAIN 
In the “Mendelian white” strain studied there are completely 
green and completely white plants. Albinism is here inherited as 
a simple Mendelian recessive. The green plants are entirely like 
green plants of normal strains, so far as any visible structures are 
concerned. Microscopic examination of the cells reveals a series 
of stages in plastid development which is indistinguishable from 
the series observed in normal green plants already described. 
In the white (albino) seedlings proplastids are present in the early 
embryonic stages just as in the green plants (figs. 10-12). In 
older tissues (figs. 13-16), however, corresponding to similar regions 
in a green plant (figs. 7-9), there is a striking difference in the 
behavior of the proplastids. They increase in size very slowly and 
irregularly, and although the leaf tissue itself continues to grow 
and differentiate, doubtless at the expense of reserve food stored 
in the seed, the proplastids do not develop as rapidly, or in as 
large numbers, as in the tissues in the same stages of differentiation 
in a green plant. Granules measuring 0.8—-1.2 w in diameter are 
found just as in normal green tissue, but development beyond this 
stage occurs only in a few scattered instances. The few proplastids 
which do become larger frequently present an abnormal appearance 
(figs. 14-16). In the living cells they are colorless or nearly so, 
and may sometimes have a darker irregular mass near the periphery 
(fig. 15). When fixed according to BENDA’s method and stained 
with haematoxylin, they bear a striking resemblance to small 
nuclei, and the irregular mass within these bodies bears a striking 
resemblance to densely staining nucleoli. When the tissues have 
reached a stage comparable with that at which chlorophyll appears 
in a normal green plant, there are very few plastids as large as those 
in which chlorophyll first develops in the green plant, the cell 
being characterized rather by a large number of proplastids, 4 
condition suggesting retarded development (fig. 16). There also 
occur irregularly shaped masses, giving the appearance of degenerat- 
ing plastids which had become partly mature. Figs. 14 and 15 
represent the appearance of the cytoplasmic bodies in mesophyll 
cells occurring between the vascular bundles of the leaf. Fig. 16 
shows the condition which is found in a cell nearer the bundle. 
