166 CARROLL— ON DEVELOPMENT OF 



a remarkable degeneration of potentially sporogenous tissue is proceeding 

 (Fig. 11). Plates of cells ramifying through the sporogenous mass under- 

 go this process of degeneration. Among these plates of cells appear 

 cells filled with needle crystals (Fig. 11). Similar needle crystals are 

 quite common in the wall and other parts of the different members of 

 the flower. This degeneration of pollen is generally quite extensive, 

 involving at times fifty percent of the potentially sporogenous tissue. 

 The history of the pollen is an illustration of the great amount of loss 

 suffered by originally sporogenous cells. First, the early cutting off the 

 tapetum removes a large percentage of available tissue, then the exten- 

 sive degeneration of sporogenous cells, and lastly the loss mentioned 

 above of a very considerable amount of pollen with the falling away of 

 the whorl of stamens before the total discharge of pollen. In the cleis- 

 togamous anthers the loss through the organization of the tapetum 

 involves as great a per cent as in the chasmogamous anthers; the steriliz- 

 ation through degeneration is less extensive, however, and as the pollen 

 grains have germinated before the fall of the cap, practically none is 

 lost at this stage. 



At maturity the pollen grains are identical in the two types of flowers. 

 They are oval or somewhat barrel-shaped measuring on an average 

 0.03 X 0.019 mm. The intine and exine are quite evident in the one 

 nucleate pollen grain. The exine in both types of flowers becomes 

 marked with flat-topped ridges dividing the surface into more or less 

 hexagonal areas. In the chasmogamous flowers the pollen grains are 

 sometimes loosely held together by threads. In the cleistogamous 

 flowers these threads do not appear; but if their function is to hold the 

 grains together, they would be functionless in the cleistogamous anthers 

 where the amount of pollen is very small, and it is never discharged from 

 the pollen sacs. There are easily distinguished four points of exit of the 

 pollen tubes. When germinated in sugar solution four tubes issue from 

 these points and attain a considerable growth. It was not discovered 

 whether the pollen grains on the chasmogamous stigma gave forth more 

 than one tube apiece, but in the germinating grains of the cleistogamous 

 anthers only one tube issued from a grain in the cases examined. 



The germination of the microspore is quite t}q3ical. The one nucleate 

 stage is of relatively long duration (Fig. 13). The spore coats become 

 differentiated and the exine marked with the characteristic ridges. 

 Division gives rise to a large tube nucleus and a smaller generative 

 nucleus. The tube nucleus is round and takes a position in the middle 



