STUDIES ON THE PLANT CELL. — IV. 



BRADLEY MOORE DAVJ;;. 



Section III. Highly Specialized Plant Cells and 

 Their Peculiarities {Continued). 



4. The Spore Mother-cell. 



The spore mother-cell and its homologues the pollen mother- 

 cell and certain embryo-sacs have furnished some of the most 

 interesting subjects for cell studies in the plant kingdom. 

 Sporogenesis in all plants above the thallophytes seems to be 

 a period when nu(-lear structures are esi^ecialiy clearly differ- 

 entiated and when tlie mechanism of mitosis reaches the highest 

 degree of complexilw These intricate conditions are only 

 equalled by jn-ocesses in tlic (level()i)ment of the female game- 

 tophyte of some angiosperms. and (hiring endosperm formation, 

 also in the events of sperniatogem-sis and with the segmentation 

 of the egg nucleus of certain gN nmospcrms. 



Sporogenesis is one of the critical periods in the life history 

 of a higher ])lant since it is the time when the ase.xual genera- 



])rovides certain important features such as the reduction phe- 

 nomena concerned with chromosomes and greatly atlds to the 

 interest in these cells. These matters will receive si)ecial atten- 

 tion in Section \\ hut they nnist be borne in mind to appreciate 

 fully the signirtcance of many events of spore lorniation. 



The general hi-^tor) ol the spmv mothcr-rrll ma> be (le..cril)ed 

 as follows: It is the product ot the last mitosis in the repro- 

 ductive ti.ssuc called thv are hc^porium. This mitosis always 

 presents the nmnber of chromosomes characteristic of the 

 sporophyte which is doul)le the nmnber found in the game- 

 tophyte. Therefore the nucleus that passes into the spore 

 mother-cell has the sporophyte number of chromosomes. Two 



