Study of Reproduction in the Genus Acer 127 



of the writer agree for the most part with those of the earlier 

 above-named investigator, but there are some points with regard 

 to which the writer would like to suggest a somewhat different 

 interpretation. To make these clear, a review of the situation 

 will be given. 



The ultimate origin of the megaspore mother cell was not 

 determined. In material fixed about the end of October, 1918, 

 it was already differentiated as a deeply placed cell in the for- 

 ward end of the nucellus. The first ovular coat was just becom- 

 ing evident at that time (Fig. 85). Little advance in the growth 

 occurred till spring, when a rapid increase in size accompanied 

 the growth and maturation of the stamens, and the heterotypic 

 division in the megaspore mother cell occurred soon after the 

 microspore cells had reached the tetrad state. Both of the 

 ovular integuments were well developed by the time synapsis was 

 reached (Fig. 86). This applies only to the female flowers. 

 In the functionally male flowers the ovaries remain very small, 

 and the carpels seem to fail to close completely, leaving a rather 

 large opening at the stylar end. In the functionally female 

 flowers the carpels also remain sufficiently separate at the top 

 to leave a pore between the style bases, but this opening was 

 filled by the abundant stylar hairs, whose walls seem to become 

 partly gelatinized at this point. 



Following the heterotypic division there is formed a wall, 

 separating the daughter nuclei into different cells (Fig. 87). 

 The writer was able to secure a very complete series of stages 

 illustrating the chromatin behavior during the heterotypic divi- 

 sion, which was fundamentally similar to the same series in the 

 pollen formation. In connection with the discussion of the 

 nuclear conditions in this species a megaspore prophase was used 

 to illustrate the condition where the reduced chromosome num- 

 ber was thirty-six, and the same figure, showing the thirty-six 

 paired segments nearing diakinesis, illustrates the difference in 

 size between the microspore and megaspore mother cell nuclei 

 (Fig. 34). So far there is no question as to the history of the 

 megaspore. 



In Mottier's paper the description of the succeeding stages 

 is as follows: "The upper cell divides again in a similar manner, 

 so that there are three cells resulting from the mother cell (fig. 

 5). The lower one of these three now enlarges gradually ab- 



