JOHNSON: FORM OF PIAROPUS PANICULATUS 27 
For another highly self-compatible plant there were 14 fine 
pods out of 15 long-self-pollinations and 4 fine pods to 4 short- 
selfings. 
There were a few plants that gave a high proportion of failures 
and a low number of seed per pod. These failures may have been 
due to low grades of self-compatibility or to experimental errors 
in that pollen may not have been applied when the pistils were 
most receptive or the pollen in the best condition. But every 
plant produced some pods with viable seeds to both short- and 
long-pollen. 
RESULTS OF CROSS-POLLINATIONS 
A total of 33 plants were involved in the cross-pollinations 
that were made. Of 100 crosses with pollen of long stamens, 
62 produced pods with seeds per pod ranging from 2 to 58 and an 
average of 24. The 73 crosses involving short-pollen gave 50 
pods with seed per pod ranging from 4 to 59 and with an average 
of 30. Among the crosses there were five reciprocals which 
yielded pods and seeds in each of the four pollinations possible 
between them 
In all but 5 of the crosses that failed only one flower was used 
so that no definite evidence exists of the presence of cross-in- 
compatibility in these plants. The resultsindicate a very general 
cross-compatibility. 
MEASUREMENTS OF POLLEN 
H. Miiller (1873) reports decided differences in the size of 
pollen from the different lengths of stamens in the three forms of 
Lythrum Salicaria (see also Darwin, 1877). Darwin (1877) 
reports such differences based on average measurements for 
pollen in a species of Pontederia. Such differences are reported 
for Pontederia cordata by Halsted (1889) and by Hazen (1918). 
In these cases the pollen of long stamens is found to be larger 
than pollen of short stamens while the pollen of mid-stamens 
is intermediate in size. 
In making the measurements here reported pollen grains from 
several anthers and from several flowers of each plant were 
mounted in water and numerous measurements made to deter- 
The pollen of long stamens measured 
mine the ranges in size. 
Only 
38-88 wu in length and from 32-70 p in short diameter. 
