Denniston—Growth and Organization of the Starch Grain. 691 
him that all growth takes place in the interior of the grain, 
and that it proceeds from the surface inward. 
The third view, which is universally accepted at the present 
day, is that the starch grain grows by the addition of concen¬ 
tric layers. ITitzsehe (11), in 1834, noted that the outer layers 
were more resistant to acids and alkalies than the inner 
and did not consider that the last layers formed need necessa¬ 
rily he less resistant. Cruger (4), ,in 1854, made the highly 
interesting suggestion that a layer of substance between the 
grain and the plastid is a starch-forming substance. This view 
is strikingly in harmony with the facts brought out on mate¬ 
rial carefully fixed and stained by modern cytological methods 
as described in this paper. 
The question of the permanence of the plastid about the 
entire grain is closely associated with that of its method of 
growth. Schimper (35, 36), in 1880 and 1881, studied the 
starch in the cortical parenchyma of the stem of Philodendron 
grandifolium and the medullary parenchyma of Peperomia 
stenocarpa and concludes that these grains are invariably 
found at first enclosed entirely by plastids; but the material 
of the plastids is soon broken through and the starch grains 
project freely into the protoplasm. This conclusion of 
Schimper J s is probably incorrect and due to the fact that on 
large starch grains the plastid becomes so thin on the anterior 
portion of the grain as to be visible only with difficulty. In a 
later paper, Schimper finds that when starch formation is 
most active the plastid may disappear to an almost invisible 
remnant and may again regain its former size when starch for¬ 
mation ceases, but he did not change his views as to the ability 
of the starch grain to project freely into the surrounding pro¬ 
toplasm. 
He states that in the large eccentric grains of Dieffen * 
bachia the growing end is the one upon which the plastid is 
fastened, and that when a portion of the starch grain projects 
freely into the cytoplasm and conies in contact with a second 
plastid an addition of layers may be made at that point also. 
In this way he accounts for the peculiar branched grains found 
so commonly in this plant. It seems quite probable that the 
