672 Wisconsin Academy of Sciences, Arts, and Letters. 
saturated, and it is on this side that the thick portions of the 
starch layers are deposited. This assumption is in harmony 
with the fact that, when the eccentric layers begin to form, 
they are simply thinner on the anterior end^ then they become 
incomplete, and finally are laid down on the posterior end only. 
The question as to the existence of a specially defined outer 
layer of the starch grain was early raised and has been dis¬ 
cussed by various authors. Fritzsche (11, p. 138), in 1834, 
was one of the first to point out that the peripheral part of 
certain varieties of starch grains shows a somewhat different 
reaction to stains than the central portions, and supposed it to 
be due to the presence of certain foreign matters, in this layer 
which render it more resistant. 
Fageli (24, p. 186]^ in a paper published in 1847, held 
that the outer part of the starch grain is composed of cellulose. 
This, however, was soon disproved. Criiger (4, p. 41), in 
1854, described a layer between the protoplasm and the starch 
grain which “does not stain with iodine, nor does it stain 
brown as readily as the surrounding protoplasm! 7 As he 
makes no mention of the plastid in other connections, it is pos¬ 
sible that this is what he saw, and his figures bear out this 
view. 
In 1885, Mikosch suggested the existence of an intermediate 
region between the grain and the plastid, which is filled with 
the so-called “mother substance” for the grain. Mikosch’s 
conception agrees well with what I have described below as the 
specially differentiated peripheral layer. Meyer (18, p. 149) 
denies the existence of such a mother substance and says that 
normal starch grains do not possess a specially differentiated 
outer layer, but that he found such a layer in a few cases in 
starch from a potato. 
Such a layer is described by Salter (32, p. 40), who believes 
that it is composed of starch but that it is denser than the re¬ 
mainder of the grain. This density is due, according to 
Salter, to the fact that the loose layers become much thinner 
at the periphery of the grain, hence the peripheral portion of 
the grain is made up chiefly of the dense layers which join and 
run around the hiliun in large eccentric grains such as those 
