266 



THE AMERICAN NATURALIST [Vol. XL 



(lisaj)i)oar.s so coiiipletely as not to be reco^jnizable at all. Second, 

 it is said that the jjollen grain of Picea always forms "normally" 

 two })rothallial celis which disintegrate more or less, hence when 

 only one is fonnd the other mnst have disappeared. Some va- 

 lidity must of course be granted to the first reason given. It is 

 {)robal)ly true in some cases, but it is absolutely impossible to 

 prove its truth in a given case, hence the number of cases in which 

 it is true is j)urely a matter of conjecture. As to the second reason 

 given, it is a conclusion based on observation, and cannot be used 

 to prove the correctness of the observations upon which it rests. 

 Back of it lies the assumption that the "normal" is invariable, 

 an assumption which is far from the truth. Even if some pollen 

 grains of Picea have been shown to form two disintegrating pro- 

 thallial cells, it does not at all follow that they do so invariably. 



Fig. 4 rPl. 1) shows a pollen grain in which there were undoubt- 

 edly three disintegrating prothallial cells. All of them were per- 

 sistent, and separate from each other, and from the antheridium 

 part of the pollen grain, so that there was no difficulty in recog- 

 ni/inu' tlie nuiiiher certainly. This o-rain was at the stage pre- 

 cediii.u- the division which s(>|)arates the sialk and the central cell. 

 Thr thinl .li.Mntegrating eell cannot l>e interprete.l as a stalk cell, 

 first, because it so closely resembles the other disintegrating j^ro- 

 thallial cells in size and appearance, and second, because it is so 

 completely se{)arated from the dome-shaped cell to which it would 

 be closely attached if it were a stalk cell. 



Fig. 5 (PI. 1) shows a variation in the position of the prothallial 

 cells, though their number is "normal," that is, two. In Fig. () 

 (PI. 1) there is a variation in both the innni)er and the position. 

 Three pollen grains were s,>en like Fig. :,. l.ut only one like Fig. (\. 

 The latter shows without any donbt whatewr a ca^e of three 



