102 MEMOIRS OF THE NEW YORK BOTANICAL GARDEN 



and eight-celled colonies of P. Boryanum, such form relations 

 cannot, of course, be taken as giving any full expression of the 

 constitution of a true biological type for the species. Such a 

 type must represent many other characteristics of function and 

 life history. It is interesting, however, to note that the form of 

 the cells and their arrangement in more or less regular concentric 

 series which results in a plate-shaped colony have been regarded 

 by the critical students of the genus from the earliest times as 

 the most reliable diagnostic characteristics both for the genus 

 and the species, the form of the colonies and the arrangement 

 of the cells being the basis of the genus and the inherited form of 

 the cells the basis for the delimitation of species. The configura- 

 tion in such a diagram represents the form the most vigorous 

 individuals tend to assume when placed under the most favorable 

 environmental conditions and such a type represents the maximum 

 potentialities of the germ plasm of an individual or group under 

 such conditions. The determination of such types makes it 

 possible to distinguish the morphogenetic value of the specific 

 organization of an individual or group as contrasted with the 

 effects of environmental influence. 



It may seem that in characterizing such a schematized con- 

 figuration as the type of a whole series of endlessly fluctuating 

 individuals there is a return to the vagaries of the ideal morphology 

 of the beginning of the last century and it cannot be questioned 

 that the evidence that the organization of the Pediastriim colonies 

 is determined by fundamental principles whose perfect and com- 

 plete expression is conceival)le but is rarely if ever realized justifies 

 in some degree the recognition of predeterminable and ideal types 

 of structure. It is to be remembered, however, that the organiza- 

 tion here involved is based on the physical properties of the 

 substances concerned rather than any such abstractions as the 

 principle of perfecting metamorphoses or even of predetermined 

 harmonies. 



Such tyjX's, of course, have little to do in many cases with the 

 so-called nomenclatorial and historical types recognized in rules 

 of nomenclature. It may, of course, be even a matter of accident 

 whether the first specimens of a species that are discovered will 

 happen to be biologically typical of the group to which they belong, 

 and it is conceivable that with rigid adherence to a doctrine of 



