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 outercells 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. 



