430 HARPER— ORGANIZATION, REPRODUCTION 



vision, the centrosome, blepharoplast, plastids, pyrenoids, etc., of 

 Tefradesmus ('13), Scenedesmus ('14), Characium ('16), Pedi- 

 astrum ('16), etc., is needed before we shall be able to correlate 

 the evidence for cell polarities, adhesions, growing points, surface 

 tension, etc., with the data from the chemical study of colloids. But 

 it is obvious that it is only on the basis of such studies that we can 

 hope to lay the foundations for a proper theory of the hereditary 

 transmission of characters and the morphogenetic processes by which 

 a mother cell is transformed into a mass of free-swimming swarm- 

 spores and these in turn into the adult colony of P ediastriim. 



Inheritance of the Characters of the Colony. — The characters of 

 the colony as a whole, however, may seem to involve a much more 

 indirect and hence perhaps properly a factorial representation in the 

 germ cell, but such a conclusion seems to me quite unwarranted. 

 I have elsewhere in a number of cases emphasized the incommensu- 

 rability of the organization of the cell and that of the many-celled 

 body. Driesch ('05) has shown the impossibility of a preformation 

 which demands even the simplest possible three-dimensional repre- 

 sentation of the organization of the adult in the organization of the 

 germ plasm. 



The characters of the colony as a whole are dependent, as noted, 

 directly on the form, polarities, adhesiveness, surface tension, etc., 

 of the individual cells. These are characters of the cells as wholes, 

 as protoplasmic aggregates, and there is no reason for conceiving 

 them as especially represented in localized regions of the chromo- 

 somes, at least in the case of these simple plants. 



We cannot compare cell characters of form with colony char- 

 acters of form except in the case of some of the simplest surface- 

 tension relations. The colony is an aggregate of cells whose organi- 

 zation is an expression of their cellular interactions in ontogeny. 

 The form characters of the colony may be transmitted down to the 

 details of cell arrangement, shape of intercellular spaces, etc., but 

 these details cannot be conceived as in any way directly represented 

 in a germ plasm. 



The complexity of the adult colony is the expression of the dif- 

 ferentiation made possible by the interaction of individual cells and 

 their specialization along different lines. An example is found in 



