158 The Ottawa Naturalist. [March 



any large body of water. In other words, much heat drives 

 away water, and much water prevents warmth. To have plenty 

 of moisture a plant must be surrounded by water. To have 

 plenty of light and heat it must be out of water. How can these 

 contradictory needs be properly met? 



Simple green plants of only one or a few cells might float on 

 the surface of a body of water, enjoying plenty of light and water, 

 but the temperature would be lower than "that which is most 

 stimulating to their life-processes. If they drift ashore the heat 

 of the sun will soon remove the water necessary to their life, in 

 spite of the wall of cellulose they construct about themselves. 

 Some new arrangement is necessary. Protoplasm responds to 

 this challenge by keeping the offspring close together, until a 

 mass is formed. The inner ones are kept from the drying air 

 by the outer ones, which are soon destroyed, becoming empty 

 cells, but forming a more or less waterproof and non-conducting 

 coating. This method is another permanent victorv o\-er 

 threatening conditions because we find that every kind of creature 

 living in air has adopted this plan of an epidermis. 



But in this mass of cells, each one demands an equalitv in 

 exposure to light, warmth and moisture if all have the same 

 work to do, so we find that they have gradually adopted some 

 definite arrangement, regular and symmetrical. It is quite 

 evident that if everv cell is to be independent of everv other cell, 

 it must be equally exposed to beneficial conditions. This perfect 

 socialistic condition is consummated in Volox a svmmetrical 

 sphere which rotates slowly in the water. It is evident that a 

 small sphere is the climax in this direction, as in a larger one the 

 inner cells would be beyond the reach of light, and possiblv of 

 moisture, and even such a sphere must remain in water in order 

 to rotate. 



There seems no further progress possible in the face of these 

 opposing conditions. How can anything better be produced? 

 Here Protoplasm had to strike out a new line of progress. We 

 describe it briefly as Division of Labor. The first evidence we 

 have of this is in such small plants as Riccia, floating on still 

 water or living on damp soil. Their mass of cells may be com- 

 pared to the spherical Volvox, but instead of rotating and 

 exposing every surface to light, one side of Riccia is permanentlv 

 set aside to absorb light and air, while the other is devoted to 

 the absorption of water. This division of labor may seem a 

 small advance, but it contains a prophecy of everything we find 

 in the structure of the tallest tree. 



The dorsiventral arrangement proved itself a success, and 

 larger land plants of similar arrangement and structure were 

 produced, with an elaborate epidermis and ventilating svstem: 



