No. 472] 



POLLEN GRAIN VARIATION 



257 



cell, the latter bulging into the former. The smaller cell divides 

 again into two unequal cells, the smaller lying against the pollen 

 grain wall, the larger one being hemispherical. IVIost pollen 

 grains are ripe at this stage of development, and undergo no further 

 changes till the time of fertilization. Often, however, one meets 

 a pollen grain which does not remain at this stage of development, 

 but goes a step farther in that the hemispherical cell divides once 

 more, so that a three-celled body is found in the interior of the 

 pollen grain. Juranyi's Figures 3 and 8 of Plate 33 (72) show 

 very well what he found. He, as well as Hofmeister, was mis- 

 taken as to the divisions of the smaller cells, since later investiga- 

 tions have shown that the small cells are cut off successively from 

 the larger one and that only the last of the smaller cells divides 

 when the "stalk" and "body or central" cells are formed. Jur- 

 anyi's figure (72, PI. 33, Fig. 8), which shows tiiree small cells, 

 may either be an actual variation in the number of cells, or it may 

 be a case of premature division into "stalk" and "central" cells. 

 No certain conclusion can be reached, but if the division into 

 "stalk" and "central" cells is the same in Ceratozaiiiia Wt'hher 

 found in Zamia, then Juranyi's figures of the tortiicr iiniH ate 

 a variation in the number of prothalHal cells or v\>v a two-celled 

 stalk. In 1S82, Juranyi reported that he had se(Mi a U-w cases 

 among the Cycadacea' in whicli the small colls could divide parallel 

 to the long axis of the prothalliiun (Vorkeim), an<l that in Larix 

 europwa he found some })ollen grains in which the prothallium 

 ended with two cells lying beside each other, and separated by a 

 division wall. The upper cell had divided parallel to the long 

 axis of the prothallium. In the cases just mentioned in which 

 the small cells in some of the Cycadacefe divide parallel to the 

 long axis of the })rothalliuni, it cannot be questioned that we have 

 a case of variation from the normal, both as to the number of cells 

 formed, and as to the relation of those cells to each other in space. 

 In the cases of Larix europcea in the upper c(>ll there may have 

 been an earlier division than usual into ihc two -^perm cells, though 

 at the time these observations were made the exact ori^m ot the 

 sperm cells was not understood. 



Strasburger. in Die Cnnl/rrrn innl (hirium n , 72 i added much 

 to our knowled-e of these plants, thou-h some of his observations 



