666 
MOLECULAR FORCES IN THE PLANT. 
as before ; it is therefore probable that the extracted substance lay previously 
between these micellae without being contained in them. This view is also more or 
less probable in the case of chlorophyll-granules and protoplasm ; in the former the 
fundamental protoplasmic substance remains behind as a very solid skeleton when 
the green colouring matter is extracted by ether, alcohol, oil, &c. Very different 
substances are certainly combined in the protoplasm ; and when a naked primordial 
cell secretes a cell-wall, it may be assumed that -the micellae which form the cell-wall 
w^ere previously distributed between those of the protoplasm, and only change their 
position and their chemical nature when they are secreted in the formation of the 
cell-wall^ ; the protoplasm which remains behind retaining essentially its original 
properties. The same is the case when grains of starch or chlorophyll-granules 
are formed in the protoplasm. A fundamental substance is clearly present in the 
protoplasm which always retains the essential properties of protoplasm ; but various 
other substances penetrate between its micellae which are afterwards excreted. This 
is especially observable in the formation of zygospores and swarmspores. 
The nutrition and growth of organised structures takes place, as has already 
been shown in Book I, by intussusception ; the nutrient solution penetrates between 
the micellae already in existence, and either occasions by apposition an enlarge- 
ment of the individual micellae, or new micellae of small size are produced in the 
spaces filled with water, which then increase by the apposition of new matter, or the 
increase takes place in both ways at different points. The increase in surface of the 
cell-wall, starch-grain, &c. is therefore brought about by the micellae being forced 
apart from within. Connected with the growth of the micellae already in existence 
and with the formation of new ones is a continual disturbance of the osmotic equi- 
librium between the surrounding fluid (the cell-sap in the widest sense of the term, 
see p. 62) and that within the body, M'hich has the effect of constantly drawing fresh 
particles from the surrounding fluid to the interior of the body which is undergoing 
augmentation. 
Chemical processes in the interior of the growing body are also always con- 
nected with these processes of growth. The nutrient fluid which penetrates from 
without contains in fact the material for the formation of micellae of a definite 
chemical nature ; but this material is chemically different from the micellae which 
it produces. Thus starch-grains are nourished by a fluid which clearly does not 
contain any starch in solution ; and again the cell-wall grows by the absorption of 
substances out of the protoplasm which are not dissolved cellulose. The colouring 
matter of the chlorophyll arises in the interior of the chlorophyll-granule; and the 
substances by which the protoplasm is nourished by intussusception are clearly 
only produced in the interior of the protoplasm, as is shown in particular by naked 
Plasmodia and by unicellular Algae and Fungi. Growth by intussusception is 
therefore connected not only with a continual disturbance of the molecular equi- 
librium, but also with chemical processes in the interior of the growing structure. 
Chemical compounds of the most various kinds meet between the micellae of an 
^ [According to Schmitz (Sitzber. d. Niederrhein. Ges. f. Natur, und Heilkunde, Bonn, 1880), 
the cell-wall is formed, at least in the cases which he observed, by the actual conversion of a 
peripheral layer of protoplasm into cellulose.] 
