platp: XII 



Figure 80. — Section of megaspore mother-cell with surrounding; 

 cells, showing- spindle of first reduction-division. Eight chro- 

 mosomes were counted in this spindle, four of which are shown 

 in the figure. X 800. 



Figure 81. — Portion of section of megasporangium, showing the 

 unusual condition of tlie four potential megaspores in a row, 

 the two upi^er already being resorbed. Or, judging from the 

 very indistinct wall separating the two lower cells and from 

 their size, this may be a case where only three megaspores 

 \\'ere formed, and the lowest has undergone the first division. 

 X 800. 



Figure 82. — Portion of section of megasporangium, showing omission 

 of formation of wall between the two outer potential megaspores, 

 these and the next, lower becoming resorbed. X 800. 



Figure 83. — Portion of section of megasporangium showing young 

 embryo-sac with two nuclei ; upper potential megaspores and 

 part of surrounding tissue becoming resorbed. X 800. 



Figure 84. — Young embryo-sac with four nuclei; showing also 

 remnant of upper potential megaspores. X 800. 



Figure 85. — Mature embryo-sac, showing synergidae, upper polar 

 nucleus, egg, lower polar nucleus, and antipodals. X 800. 



Plate XII 



in pouch at base of 



Figure 86.— The three antipodal cells lying 

 nature embryo-sac. X 800. 



Figure 87. — Pollen mother-cell, synapsis stage. X 800. 



Figure 88. — Young pollen-grain in tetrad before the dissolution of 

 the tetrad wall. X 800. 



Figure 89. — Pollen-grain just before formation of generative cell, 

 showing enclosed starch grains and beginning of wall thicken- 

 ings. X 800. 



Figure 90.— Pollen-grain showing spindle preparatory to formation 

 of generative cell. X 800. 



Figui'e 91.^Cross section through middle of pollen-grain at stage 

 sliown in figure 90. X 800. 



Figure 92.— Pollen-grain just after formation of generative cell. 

 X 800. 



Figure 93.— Longitudinal section through almost mature pollen-grain, 

 showing tube-nucleus and generative cell just previous to form- 

 ation of male cells. X 400. 



nature pollen-grain showing 

 nd the degenerating tube- 



Figure 94.— Longitudinal section of 

 the two male cells still united, , 

 nucleus. X 375. 



Figure 95. — Longitudinal section of mature pollen-grain, showing 

 characteristic dumbbell shape. X 175. 



Figure 96, a and b. — Surface and profile views, respectively, of the 

 ]iollen-grain wall thickenings, at mature stage. X 800. 



Figure 97.- Pollen-grains, during the dissolution of the tetrad walls 

 and formation of the pollen-grain wall. X 800. 



