Denniston—Growth and Organization of the Starch Grain . 677 
that in such watery tubers the peripheral layer never passes 
into typical starch. 
In the cases of Phajus :J Dieffenbachia and Pellionia, the 
plants from which the starch preparations were made were ac¬ 
tively growing. In the commercial starches, the method of 
cleaning and preparing will certainly have much to do with the 
presence or absence of any peripheral portion of the grain, as 
well as the relative maturity of the parts of the plant from 
which the starch was taken. 
In the case of pea starch, no peripheral layer could he dem¬ 
onstrated, and it is possible that the starch matures more 
rapidly in this plant than in the others studied. Bean 
starch showed but few grains with an outer differentiated 
layer. These were grains of small size and probably imma¬ 
ture. 
In preparations of Ganna which show the starch grains 
to be partially dissolved by natural corrosion by diastase, an 
orange layer appears quite constantly at the periphery of the 
portion of the grain remaining. The width of this orange 
layer is usually quite uniform although but a fragment of the 
laminated grain may remain inside. The structure and ap¬ 
pearance of these corroded grains will be more fully discussed 
below. The fact that we have orange-staining layers in grains 
in process of solution as well as in grains in process of forma¬ 
tion throws further light on the nature of this material as a 
transition substance. 
The appearance of the so-called strata or concentric layers 
of the starch grain as seen when mounted in water has been 
variously characterized by different authors. Strasburger de¬ 
scribes the layers as appearing to contain varying amounts of 
water, and as separated by dark limiting lines. Meyer dis¬ 
cusses the varying appearances obtained by focusing through 
the grain with low and high magnifications, but gets no new 
data as to the composition of the layers. Salter uses the 
terms “dense” and “lax” to describe the layers of the starch 
grain. 
I have naturally found the median optical section of the 
grain the most favorable for study, and my descriptions are 
