102 BOTANICAL GAZETTE [FEBRUARY 
in the prophase, but occasionally the first spindle is formed, though 
it is irregular. Development never proceeds to a later stage. The 
sterility is here a Mendelian character, recessive and correlated with 
a certain somatic character, the two always appearing together. 
TISCHLER (31) ascribes the sterility of the hybrids of Ribes and 
Bryonia, as well as those of Lathyrus odoratus, to the influence of long 
culture. He studied three hybrids of Ribes: (1) R. intermedium= 
R. sanguineum XR. nigrum; this hybrid is fertile, producing 10-15 
per cent. good pollen grains; (2) R.Gordonianum=R. aureum XR. san- 
guineum; absolutely sterile and showing great vegetative luxuriance; 
(3) R. Schneideri=R. grossulariaXR. nigrum; sterile. He finds a 
splitting of the spirem in the strepsinema stage, and that the chromo- 
somes when formed lie in pairs in the prophase. As in O. /aia, the 
heterotypic is a reduction division, the homotypic an ordinary equa- 
tion division, and the chromosomes split (longitudinally) in the ana- 
phase of the first mitosis. In all the hybrids, as well as in the parents, 
e.g.,R. sanguineum, the reduction divisions are mostly normal, 
though in R. Gordonianum occasional extra spindles are found in the. 
cytoplasm; otherwise its tetrad divisions cannot be distinguished from 
those of R. intermedium; but the sterile grains do not grow in size. 
The first evidences of degeneration appear then in Ribes later than in 
any of the others mentioned, 7. e., usually after the reduction divisions 
are completed. 
In a sterile hybrid of Begonia alba 2B. dioica 4, TISCHLER (32) 
finds that when the reduction divisions in the pollen mother cells are 
irregular, they are invariably preceded by abnormalities in synapsis; 
but that when synapsis is accomplished regularly the reduction 
divisions are also carried through without irregularities. There is 
often unequal division of the chromosomes on the heterotypic spindle. 
In the tetrad divisions, chromosomes in the cytoplasm and extra 
nuclei are relatively seldom found. The pollen grains are very often 
degenerate and of unequal size. In the female gametophyte the 
megaspore mother cells divide normally, but the embryo-sac mother 
cell degenerates. Whether another embryo-sac is formed later from 
the sporophyte tissue, as shown by TISCHLER for Cytisus Adami (29), 
Ribes Gordonianum, and Syringa chinensis (30), has not been deter- 
mined. 
