1908] BURLINGAME—PODOCARPUS 175 



characters or, in cases where they occur only occasionally, that it is a 

 reversion to ancestral conditions. Juel (6) has already suggested 

 this explanation for the case of Cupressus, and has even gone so far 

 as to suggest a possible sequence in the reduction. At this point 

 one must be on guard against supposing that types which illustrate 

 this reduction series necessarily, or even probably, stand in the same 

 series phylogenetically. It seems to the writer that if this funda- 

 mental principle be firmly grasped, it is entirely unnecessary to sup- 

 pose that because Podocarpus and Pinus are clearly related and 

 because Pinus is older historically, therefore the multiplication of 

 prothallial cells in Podocarpus must be coenogenetic. One need but 

 assume that both are derived from a common ancestral stock and that 

 one has retained the prothallial complex and the other has lost it. 

 Of course if one believes that Podocarpineae have come directly out 

 of living Abietineae, this explanation would not hold. While it is 

 true that the latter are known as far back as the Carboniferous (4) 

 and the former are not known to be nearly so old, it is equally unde- 

 niable that we know but little of the plant remains of those parts of 

 the world in which their remains would be most likely to be found. 



Summary 



1. There are in the species of Podocarpus studied two prothallial 

 cells which may or may not divide. There may be as many as eight 

 prothallial cells in two tiers derived from the two primary ones. 



2. Division in the prothallial tissue is mitotic and the prothallial 

 cells do not degenerate. 



3. There is a stalk cell and a body cell, sometimes differing very 

 little from one another in appearance; whether both may produce 

 male cells is yet uncertain. 



4. The number of chromosomes is twelve and twenty-four. 



5. There may be a variable number of cells or free nuclei in the 

 pollen grain at the time it is shed. 



Acknowledgments are due to Professors John M. Coulter and 

 Charles J. Chamberlain of this laboratory for valuable advice and 

 criticism during the progress of this investigation. 



The University of Chicago 



