ANATOMY OF TISSUES. 43 
in any plant, as during its life it is subject to continued changes 
in which the origin and development of various tissues are in- 
volved. Again, the application of the word varies with the 
standpoint from which we use it. Thus we may say of a plant, 
in reference to its growth, that it consists of two tissues, merz- 
stematic and lasting tissue. Each of these may be subdivided in 
respect to other functions. If we follow the changes undergone 
by any plant of high organization during its development, the 
history and character of all kinds of tissues will be made clear ; 
and afterward, a knowledge of their distribution in the various 
classes of plants is easily obtained. 
2. Origin and Partial Development of the Principal Tissues 
and Systems. 
The successive stages of development in the fertilized egg- 
cell of a dicotyledonous phanerogam may be described as follows. 
A wall is formed dividing the cell into two; others follow in 
rapid succession at various angles and in all three directions, 
making a rapid increase in the number of cells. At first all 
these are similar in form and all are capable of division. ‘This 
continues, however, only for a short time and then localization 
of growth takes place; that is, a certain number of cells retain 
their. power of division while the remainder lose this ability, 
being able to increase in size but not to form new cells. This 
gives us the first division into tissues, meristematic tissue, or 
dividing cells, and lasting tissue, or cells not capable of division. 
The meristematic tissue forms the localized centres of growth, 
which are at this stage two in number, namely, those of stem 
and root, and they occupy the opposite ends of the oval or 
slightly elongated body. As .growth continues, the lasting 
tissue constituting this body is constantly added to by the new 
cells developed from the meristems and is thus increased in size 
and number of cells. Very soon after the origin of these two 
