135 



Observations upon Pollen Measurements. 



* 



Of forty-one kinds of pollen taken at random and included in 

 twenty orders, sixteen were isodiametric or spherical in shape, 

 while twenty-five were with unequal diameters and generally 

 oval in outline. The ranse in size in the isodiametric sorts was 

 from 13-17 yu in Oiiosmodinm molle to i lO-i 17 // in Geraniwn 

 macidatiim, and 130-138// in (Enothera biennis, which latter has, 

 however, a spherical center with a number of large broad projec- 



tions. 



In the groups with unequal diameters the range of sizes is 

 practically the same as given above, namely: 13-20/^ by 27-37 ;i 

 in Sjeirojmna hmcolata to 45-50 /< by 120-135 /< in the Day Lily. 



In making the record for each sort, the shortest as well as the 

 longest distance was taken in each case and the grains were 

 measured dry and again after becoming thoroughly wet with 

 water. 



Returning to the spherical group, the average of all the short- 

 est diameters for the whole sixteen is 57.7 yU and for the longest 

 ^^.1}A, thus giving a range of 8.6 y/. By taking the similar 

 parallel series of measurements for wet grains the average for the 

 shortest diameters is 68.6/^ and the longest 74.5 //, or a variation 

 of 5.9 //. The average of the two averages for the dry measure- 

 ments give 62 ^, while the same of wet grains is 71.55 ;^. thus 

 giving the increase from the addition of water of 9.55 yi, or 15.4%. 



Turning now to the oval group, the average of the short 

 diameter is 26.2 /< and of the long 48-4/^; the same when wet 

 are 34.9 /^ and 42.5 /< respectively. In other w^ords, there is 

 33-2% increase of the short diameter in the wetting, while the 

 decrease in the longer diameter is J 2.2% ! 



Pollen when dry, that is, freshly taken from the dehisced 

 anther, shows some things not seen in the same after it has 

 become wet. Of course the natural shape of the dry pollen is 

 destroyed by the wetting process— as the above figures plainly 

 show. Many grains have characteristic folds which are lost from 

 view when liquid expands the coats. Only one of these folds is 

 usually seen in side view, but b y looking at one end there are 



♦ Read at the Cleveland meeting of the A. A. A. S., Aug., 1888. 



