218 VEGETABLE PHYSIOLOGY 
development of succulent parenchyma. During the second 
year they have a much smaller foliar development, but each 
sends up its flowering stem. The constructive activity is 
much less than during the previous year; the root gradu- 
ally dwindles as the fruit and seeds develop, the store 
deposited in the succulent parenchyma being applied to 
their formation and maturity. 
Based upon considerations such as these, we may make 
a further classification of the nutritive substances which 
exist in the body of the plant. We can speak of those 
which are used in the cells where they are formed, and of 
those which are removed therefrom for the feeding of the 
other protoplasts. These, again, may be devoted to imme- 
diate use, or may be stored as reserve materials for deferred 
consumption. We can recognise in every plant some kinds 
which are suitable for transport from cell to cell, and others 
which are not able to pass through cell-walls, but must: 
remain in the position in which they are formed. These 
two classes of circulating and stored food-stuffs have an 
intimate relationship to each other, and must be mutually 
interdependent, each being reinforced by the other accord- 
ing to the needs of the particular moment. 
If now we turn from these general considerations to 
the sequence of events that are normally taking place in 
the cells which contain the chloroplasts, we can form some 
definite idea of the course of the processes of construction 
of the carbohydrates and removal of the products. In 
such a cell there is, during favourable conditions, a manu- 
facture of sugar which is continuous and rapid. The 
cell itself needs a certain amount of such sugar for its 
own nutrition, but only a very small part of what is being 
made. The sap of its vacuole soon contains a large excess 
of sugar, and if nothing further transpires the process of 
manufacture must stop. But the cell is in contact with 
others, in many of which, perhaps in all, a similar manu- 
facture is taking place. The ordinary processes of diffusion 
or secretion tend to equalise the amounts in any contiguous 
