128 Arlow Burdette Stout 



Meleagris, Najas major, Triticum vidgare, Tradescantia virginiea, Vera- 

 trum album, Convallaria majalis, Leucojum aestivum, Tamus communis, 

 Carina indica, Epipactis palustris), and finds that in every case the ge- 

 nerative cell is cut off by a cell plate at the periphery of the microspore. 

 It is then set free and migrates into the cytoplasm of the vegetative cell. 

 I have not found the early stages of its formation in Carex aquatilis, but 

 its crescent or spindle shaped form (fig. 32) as it lies in the cytoplasm 

 is commonly shown in my preparations and suggests that it is formed 

 in the usual way and not by free cell formation. * 



The vegetative nucleus becomes quite large and the chromosomes 

 in it lie scattered in series about the periphery with much the appearance 

 observed in resting root-tip nuclei. The generative nucleus gradually 

 becomes more spherical. During these changes the pollen grain enlarges 

 considerably and its central portion is occupied usually by one or more 

 large vacuoles. This increase in size will be appreciated from a com- 

 parison of figures 30 and 33. The generative cell and the vegetative 

 nucleus now usually lie near each other and near one side of the pollen 

 grain. The chromosomes are conspicuous, their number is plainly that 

 of the haploid nuclei. The drawing shown in figure 34 is from a section 

 through a generative nucleus in late prophase. The chromosomes are 

 spherical bodies connected in a single continuous series, in appearance 

 and arrangement quite similar to that of the prophase of the division 

 of diploid nuclei (compare fig. 34 with fig. 11). In the early stages of 

 reconstruction the nuclei appear as shown in figure 35. Although these 

 nuclei are very small the chromosomes are sharply differentiated at all 

 stages. Each male cell, when fully formed, possesses a considerable 

 amount of cytoplasm with a clearly defined membrane, as is shown in 

 figure 36. The germ cells are fully formed before the pollen grains are 

 shed from the anther. The vegetative nucleus of the pollen grain is 

 spherical in shape and it usually lies near the large end of the pollen 

 grain. The two male cells lie embedded in the cytoplasm of the vege- 

 tative cell. Their nuclei are spherical with the individual chromosomes 

 as noted rather clearly defined. The central part of the pollen grain 

 is coarsely vacuolated and the germ cells lie near the walls of the pollen 

 grain. Usually they are not far from the vegetative nucleus and are 

 often on opposite sides of it. 



The vegetative nucleus of the microgametophyte is of about the 

 same size as the nuclei of the somatic cells in the root tip, as will be seen 

 from a comparison of figures 33, 35, and 36 with figure 4. The male 

 nuclei are smaller. The chromatin in them is present, however, as distinct 



