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 théir 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 
Pollen grain at the time it is shed. 
the 
Acknowledgments are due to Professors JoHN M. COULTER wee 
Cc ea J. CHamBeErtatn of this laboratory for valuable advice and 
“riticism during the progress of this investigation. 
Tae Universtry or Curtcaco ; 
