6 BOTANICAL GAZETTE [july 



Figs. 5-10 are from drawings of other nuclei at this stage of develop- 

 ment. In the majority of cases one or two smaller nucleoli occur 

 in addition to a single large one, but rarely (fig. 6) two large nucleoli 

 of equal size may be found; and very frequently the number of small 

 bodies, of equal or unequal size, may be greater, reaching as many as 

 five or six. Figs. 5, 7, 8, g show these in various stages of fusion with 

 each other and with the large nucleolus. 1 They are thus not in any 

 sense autonomous bodies. It appears that usually these fusions 

 take place until only one large nucleolus and one or two smaller ones 

 are present during synapsis and diakinesis. But occasionally the 

 fusions do not take place, and several of these bodies may then be 

 present in the later stages. The number of these nucleoli finally 

 present depends, then, largely upon the amount of fusion which has 

 previously taken place between them. In the later stages one large 

 nucleolus is almost invariably present and usually a smaller one 

 bearing a certain proportion to the larger in size, though the latter 

 may vary in size and number as already stated. There is usually 

 a clear area around the large nucleolus, as in the earlier stage, and 

 threads of the reticulum may or may not cross this and appear to be 

 attached to the nucleolus (fig. 4). The reticulum of the cytoplasm 

 usually stains rather more deeply at this time than that of the nucleus. 

 It may as well be stated at this time that in the resting nuclei of the 

 pollen tetrad and in the nuclei of the nearly mature pollen grains of 

 Oenothera one finds (fig. 11) the same condition of the nucleoli as 

 in the mother cells, namely, usually one large and one small nucleolus 

 bearing a rather definite size relation to each other, with sometimes 

 additional small ones. 



The sporogenous rows are differentiated from the tapetum by 

 the greater growth of the cells, nuclei, and nucleoli of the former. 

 At the same time they are distinctly marked off by the formation of a 

 continuous thickened wall between tapetum and archesporium 

 (fig- 3)- It is obvious that as the cells and nuclei increase in size, 

 the nucleolus grows also. Up to the time of synapsis the mother cells 

 usually form a compact tissue, but about this time the cells begin to 



1 Miss Nichols (21 ) figures what are in all probability stages of fusion of large 

 and small nucleoli in Sarracenia pollen mother cells, but interprets them as a budding- 

 off of small bodies from the nucleolus. The budlike attachments to the nucleolus 

 frequently observed by other authors are doubtless to be explained in like manner. 



