84 ELEMENTS OF PLANT ANATOMY. 
the first to give a satisfactory explanation of the origin and 
nature of these layers. He claimed that the appearance of 
stratification was caused by a difference in the amount of water 
in the alternating layers. There are many facts which support 
this view. One of them is that if the water of the grain is made 
to evaporate the lamellated structure disappears. Since the 
time when Naegeli advanced this theory, other facts have been 
discovered which lead to the conclusion that there is no dif- 
ference in the amount of water contained in the different layers, 
and that the dark lines do not represent layers, but merely lines 
of contact between the separate lamellae. ‘This same reasoning 
is also applied to the stratification of the cell wall. 
7. Aleurone Grains. 
While starch represents the organized form of non-nitroge- 
nous reserve food, the aleurone grain is the organized form 
of the nitrogenous material. These grains were discovered by 
Theodore Hartig in 1855. They occur in great abundance in 
those seeds which contain oil instead of starch. They are mostly 
round or oval colorless bodies, though in certain seeds they are 
colored. For example, they are yellow in Ailanthus, blue in 
Zea Mays, green in Pistaciae. ‘Their size varies in different 
plants, and also in the same plants and cell. The largest grains 
are found in cells containing little starch. In the seed of Vitis 
there is a single large grain in a cell. 
The grain itself consists of an outer covering of proteid 
matter, which may enclose three different structures ; protein 
crystalloids, globoids, and real crystals. The crystalloids differ 
from crystals by the property of swelling when water is added. 
They are insoluble in water, but soluble in weak potash. As 
their name imphes, they consist of proteids, compounds whose 
chemical nature is not yet thoroughly understood. The globoids: 
are nearly spherical in shape, and consist of salts of calcium and 
