316 



Belling. 



in absolute alcohol before swelling, as they do with a trace of moisture, 

 are oblong and three -grooved, and measure 90 bj- 60 microns. The 

 empty grains are usually three -winged, and, as sections show, have 

 their walls so collapsed that the cell-cavity is obliterated. They measure 

 about 68 by 42 microns. The two kinds of poUen-gi-ains appear uni- 

 formly niLxed in the anthers. In sections of young flower- buds at a 



Vg 



# 



tM 



Fig. 8. Photograph of pollen-grains of the Velvet by China tirst-generation hybrid. 

 Scale in tenths and hundredths of a millimeter. (Prom a balsam preparation.) 



certain stage, all the pollen -grains have a cytoplasmic sac enclosing a 

 large vacuole. 



A mature microspore, or pollen -grain, is unquestionably a multi- 

 cellular individual plant of the haploid generation. If we were to 

 restrict the term pollen-grain to the mature stage, we might say that 

 in these hybrids half the microspores perish before they become pollen- 

 grains. The premature death of a definite fraction of a diploid gene- 

 ration has been unreservedly, and doulitless rightly, ascribed in the 



