270 



THE AMERICAN NATURALIST 



[Vol. XL 



instead of the double pollen grain as the basis of comparison 

 the following table shows the amount of variation. 



2 Pr. 1 Pr. No Pr. Cells Total ^PoUen°' 



Cells Cells Cells Uncertain Antheridia Grains 

 No. of antheridia 4 24 18 18 64 32 



In the group marked uncertain, the uncertainty was sometimes 

 due to inal)ility to recognize clearly the total number of cells 

 present, and in other cases the position of the wall dividing the 

 pollen grain was uncertain where it ran between the disintegrating 

 prothallial cells. Only one sixteenth of this lot of antheridia shows 

 what has been called the normal number of prothallial cells. Of 

 even more importance than this fact is the further one that in no 

 case did both the antheridia in the same double grain have two 

 prothallial cells, as should have been the case if two is the normal 

 numV)er. There were several cases in which the numbers for the 

 two antheridia Avereresj)ec-tively 2 and 1, 2 and 0, 1 and 1, 1 and 0, 

 and 0. Tn those cases in which tliere were two protliallial cells 

 in one part, and one or none in tlie other |)art of the double grain, 

 it cannot be argued that some had (lisapj)ean'il by disintegration, 

 because the two parts of a double :iraiii arc usually at about the 

 same stage of development, and tlinv i. no iva.-.n to siippo.c that 



the other. At IcaM .on'ic c.m-. .u!mU\ have beeli fouml in which 

 both j>arts of tlic (lonhic urain luid two prothallial cells, and most 

 of the (loul)lc giaiiis should have shown the same number of pro- 

 thallial cells on the two sides of the dividing wall. Since neither 

 of these conditions was found to exist in the grains examined, and 

 in the light of other facts reported in earlier paragra[)hs of this 

 article, the writer feels justified in drawing the following con- 

 clusions: - 



1. 'i'hc inunl.cr of .li.int.-nitin- prothallial cells in the pollen 

 grain of Pn-rd ,.n-rls,i L. not invariably two. and when a grain 

 is foinid uhi<h .how. onh on.' Midi .vll it not necessarily the 

 .srrnn,l prothallial cell and' d,..uM not !..■ so nanie.l. At tli." most 



