FROM ALGA TO FERN 363 
may arrange a series from algae to ferns, and from ferns 
to the higher seed-bearing plants, showing increasing 
complexity of structure. 
328. Division of Physiological Labor. The differentia- 
tion of the plant body into organs root, stem, leaf, re- 
productive organs may be considered as an expression of 
the division of physiological labor. For example, when a 
sufficiently thick cell-mass is formed the inner cells may 
be deprived of light; no chlorophyll can then develop, 
photosynthesis becomes impossible, and the outer-cells must 
elaborate all the food, not only for themselves, but for the 
inner, non-green cells as well. Roots that serve to hold the 
plant in the soil, and to take in water and minerals to be used 
in the leaves, must be nourished by food elaborated in the 
green cells. The leaves and branches must be supplied 
with water taken in by the roots, and a vascular system 
becomes necessary. So, in these and countless other ways, 
the vegetative functions become divided among organs 
specially fitted by their structure to perform them well. 
Then the reproductive function becomes confined to 
certain cells, which are nourished by the others. Repro- 
duction itself becomes complicated by the development 
of two kinds of gametes, and the introduction of cell- 
fusion as well as cell-division. 
Among plants, organization the development of defi- 
nite organs for definite work has the same kind of ad- 
vantage as the division of labor among men. The 
"jack-at-all-trades" is not as efficient at any one of them 
as the specialist. The existence of carpenters, plumbers, 
masons, tailors, architects, superintendents, teachers, 
lawyers, stenographers, doctors, means greater efficiency, 
than could be secured if everyone tried to be all of these. 
