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ANATOMY OF TISSUES. 
CHaAptTer IV.— TISSUES AND SYSTEMS. 
1. True and False Tissues. 
ONLY the lowest forms of plants remain unicellular during 
life. Ordinary plants consist of a large number of cells, differ- 
ing in form and function, all of which have originated from a 
single one by the process of division. This is true of all multi- 
cellular plants except those originating by the so-called vegeta- 
tive reproduction. In this case the new plant is detached or 
broken from the old and generally consists from the first of a 
mass of cells. 
By the term tissue, in its restricted sense, is meant an ag- 
eregate of cells more or less similar in origin, shape, and function. 
The word is, however, often used in a less definite sense to 
denote any portion of the cellular substance of a plant considered 
as an entity. 
The lowest form of what may be considered a multicellular 
plant growth consists of an aggregate of cells which were origi- 
nally free but have united themselves for a time into a single 
individual. Later these separate and continue their existence 
as single cells. Some cell-aggregates originating in this way 
have a more permanent nature, their union lasting during the 
remainder of the life of the cells. Examples of both may be 
found in the low forms of algae.t According to the degree of 
1 Certain tissues forming parts of higher plants also originate by the union 
of cells which were at first free, for example, the endosperm of seeds. This case, 
however, does not fal] under the head of colony-formation. 
