Beer, Development of the poUen graiu and anther of some Onagraceae. 311 



stage botli niitotic and amitotic divisions of the niiclei take 

 place but in older anthers the tapetal nuclei divide exclusively 

 by amitosis. Side by side with this continuous multiplication of 

 nuclei a nuclear degeneration can be observed in which the 

 nuclear membrane and nucleolus are resolved into a groiip of 

 deeply staining hbres or narrow laminae. 



These fibres are no doubt identical with those observed by 

 Meves in the tapetiim of Nijmpliapa alba. These fibres have 

 been compared by Meves to the chromidial structures found in 

 certain animal cells and this comparison has a great interest in 

 the light of Goldschmidt's recent work. 



The fibres in the tapetum of Oenothera are found to be to 

 a large extent derivatives of the chromatin of the nucleus and 

 they increase in niimber as the cell advances in age and its 

 nuclei continue to divide (fragment) and to break down. 



The interesting conclusion is^ therefore, reached that a large 

 portion of the material which replenishes the exhausted pollen- 

 protoplast has at one time or another entered into the compo- 

 sition of a tapetal nucleus. 



9. The intine is a continuous membrane Uning the entire 

 inner surface of the poUen grain. It first appears and reaches 

 its gjeatest development at the bases of the three interstitial 

 bodies whilst over the rest of the pollen grain it extends as an 

 exceedingly delicate layer. During the development of the 

 intine three thick Strands of cytoplasm connect the centrally 

 placed nucleus with the spots beneath the interstitial bodies 

 where the membrane is growing most vigoously. In Oenofhera 

 the intine gives the reactions of a pectic body but üttle or no 

 cellulose can be detected in it. In Gaura Lindhehneri and Epi- 

 lohium tctragoiium both pectic bodies and cellulose occurinthe intine. 



10. The Perforation of the closing diso of the interstitial 

 body and the disintegration of the laminae of that body have 

 been most closely followed in the pollen grains of Gaura L'rnd- 

 hcimcri. The closing diso is perforated and the interstitial 

 laminae are "eaten away" in advance of the growing intine in 

 a manner which suggests the action of a solvent, probably an 

 enzyme. 



11. In Oowthera loufi'ißora^ even when growing under the 

 most favourable conditions, many of the pollen grains become 

 arrested in their development. They all seem to advance until 

 their protoplast is completely exhausted by secretion but the 

 tapetal material is insufficient to allow all of them to carry theii' 

 development further. 



12. The mature pollen grains are surrounded and bound 

 together by "fibrils" which are derived from the special-mother- 

 cell wall. When the special-mother-cell wall breaks down it 

 forms at first a structureless mucilage which no longer gives 

 anv of the reactions of callose. Later this mucilage becomes 

 drawn out into "fibrils" and these are very resistant to solvents. 



Rudolf Beer. 



