No. 454-] STUDIES ON THE PLANT CELL. 727 



though the megaspore mother-cell regularly becomes an embryo 

 sac in some forms {e. g., Lilium). But an increasing number of 

 observations indicate that the megaspore mother-cell generally 

 develops two, three or four potential megaspores although nor- 

 mally only one of these becomes an embryo sac. 



The interest in the protoplasmic activities of sporogenesis lie 

 chiefly in the elaborate. methods of spindle formation and mech- 

 anism of mitosis, in the organization and distribution of the 

 chromosomes, in the functions and activities of the nucleolus, 

 and in the organization of the cell plate and development of the 

 cell wall. There is a very extensive literature on the spore 

 mother-cell some of which, however, merely treats the broad 

 features noted in studies of a general morphological character on 

 the development of sporophylls or floral structures. We shall 

 only attempt to consider the most important contributions, and 

 for convenience will begin our treatment with the Hepaticae and 

 conclude with the spermatophytes where the conditions are the 

 most complex. 



The Hepaticse or liverworts furnish some remarkable spore 

 mother-cells, and are now the subject of considerable interest 

 and some discussion. They were first brought conspicuously to 

 the attention of botanists by a paper of Farmer ('94) on Pal- 

 lavicinia decipiens. Farmer described a remarkable series of 

 events in this type. The nucleus of the spore mother-cell 

 became surrounded before division by dense protoplasm that 

 extended into the four lobes of the cell in the form of a four- 

 rayed star which he called a " quadripolar spindle." After its 

 development four chromatic droplets appeared in the nucleus to 

 indicate its approaching division. These chromatic droplets 

 became four chromosomes which by division were doubled in 

 number. The eight rod shaped chromosomes moved in pairs 

 towards the four lobes of the spore mother-cell. There was a 

 further division of each chromosome, making sixteen in all, and 

 the four groups of four each passed simultaneously to the poles 

 of the "quadripolar spindle" which persisted to the end. It 

 should be noted that the striking peculiarities of Farmer's account 

 lie in the division of the four primary chromosomes into sixteen, 

 and in their simultaneous distribution through a "quadripolar 



