SOCIAL ORGANISATION IN ALGAE 



141 



display a morphological differentiation of structure and a physiolo- 

 gical division of labour. In this connection, it need only be men- 

 tioned that in one species ^ of Volvox — the culminating genus in 



Fig. 73. — Three stumps of Douglas Fir trees which, in the course of many years, 

 have become overgrown and completely healed over. They are now " living 

 posts." The supply of food materials to the stumps was made possible owing 

 to their roots being naturally grafted to undamaged Douglas Fir trees, one of 

 w hich is shown in the foreground on the right. Photograph by C. A. Pemberton, 

 taken in British Columbia, Canada. 



the evolution of motile coenobia — there may be as many as 22,000 

 cells, the vast majority of which are purely vegetative in function, 

 only a few ever taking part in either sexual or asexual reproduction 



^ Volvox glohator. In an asexual individual there are 1500-16,400 cells, and 

 in a sexual individual 10,000-22,000. Vide L. Klein, " IMorphologische und 

 biologi.sche Studien uber die Gattung Volvox," Jahrh. f. wiss. Bat., Bd. XX, 1889, 

 p. 146. 



