276 PLANT AND ORGANIC CHEMISTRY 
pounds peculiar to them, and found in only one family, or in 
species closely allied to it. 
Broadly speaking, the study of plant life cannot be confined 
within the limits of the vegetable cells, since its radiations reach 
to the domains of mineralogy and animal fife. From a chem¬ 
ical point alone it would be difficult to discriminate in every 
case between the plant and animal cell. The series of animal 
gums, carbohydrates, alkaloids, and coloring-matters find 
their analogous series in plants. By the study of embryology 
it is found that alantoin occurs in animal and plant life, also 
glycogen and inosite are found in both kingdoms, and the se¬ 
cretion of some plant-leaves is a fluid chemically like the ani¬ 
mal gastric juice. 
M. Leo Errera, 1 in a recent paper on a fundamental condi¬ 
tion of equilibrium of living cells, calls attention to the thin and 
plastic condition of plant as well as animal cells at the moment 
of their formation, and their tendency to assume a form which, 
under the same conditions, an imponderable lamina of liquid 
would take, and he attributes to this fact their adaptability and 
the facility with which they change. He believes that we can 
trace to this cause the great number of organic forms, and for 
the first time unite the architecture of the cell to molecular 
physics. Only with age the cell-membrane becomes thick and 
offers a considerable resistance. 
It may be suggested that this fact is further exhibited when 
applied to the conditions obtained when plants pass from their 
younger to older stages; again, it is seen on comparing the lower 
plastic protoplasmic plants with the rigidity and firmness of the 
tissues of the higher plants, and in the change from the semi¬ 
fluid to the formed and fixed states of chemical compounds. 
The law of progression is one that regards the general good 
to the disregard of the individual; since in the death or fixation 
and crystallization of individuals the vegetable kingdom, on the 
whole, has ascended to its highest present living form, and many 
of its constituent chemical parts had long ago reached their 
pinnacle in the cycle of evolution. This concerns equally the 
changes in the vegetable-cell, and its complex molecule of pro- 
1 Comp. Rend., t. xiii, 1886, p. 822. 
