1907] GATES—POLLEN DEVELOPMENT AND MUTATION IOI 
mitosis chromatin appears in the cytoplasm, as in the Oenothera 
hybrids studied. The spindle is also sometimes multipolar and 
irregular. Several nuclei may be found in a tetrad, and also chromatin 
scattered in the cytoplasm, as in O. data. This hybrid shows a 
greater variety of irregularities than have been observed in any 
other hybrid described. 
GUYER (10, 11) found in the spermatogenesis of hybrid pigeons 
similar conditions with extra and irregular spindles and incomplete 
pairing of the chromosomes. CANNON (5) found in hybrid cotton, 
Gossypium barbadense X G. herbaceum, that degeneration of the 
pollen mother cells sometimes begins in the resting stage previous 
to synapsis. The divisions in some of the pollen mother cells are 
amitotic, the nucleolus dividing first, followed by equal or unequal 
segmentation of the nucleus and its reticulum. In the case of equal 
segmentation, pollen tetrads of normal appearance may be formed. 
Multipolar spindles, with many small nuclei, were also found. In 
fertile hybrids of certain races of peas, which obey Mendel’s law, 
Cannon (4) found no difference in pollen development between 
the hybrids and their parents. He states that there is a pairing of 
the chromosomes in the telophase of the last sporogenous division 
previous to synapsis. It should be said, however, that these two 
papers are not as complete and satisfactory as some of the others. 
ROSENBERG’S (23, 24) study of pollen development in Drosera 
longijolia obovata, a hybrid of the intermediate type, between D. 
rotundifolia and D. longifolia, but nearer D. longifolia, shows that 
some of the smaller chromosomes of D. longifolia are left behind in 
the cytoplasm in the first and second divisions, where they also form 
small nuclei. Later the greater number of the pollen grains lose their 
contents. The embryo sac development also usually stops at the 
binucleate stage. The sterile hybrid sweet peas (Lathyrus odoratus) 
studied by GREGoRY (g) show an earlier degeneration of pollen than 
the other cases cited. Portions of the spirem are often destitute of 
chromatin and the chromosomes frequently are pale, which GREGORY 
attributes to lack of nutrition. The nucleolus, he thinks, serves to 
Store most of the chromatin between the reduction mitoses. Other 
conditions simulating amitosis in the pollen mother cells are illus- 
trated. Degeneration of the pollen mother cells usually takes place 
