OF T nt * 



UNIVERSITY 



LIFE HISTORY OF PINUS 35 



As already indicated, no wall separating the daughter-nuclei 

 is formed at the close of the heterotypical division in Pinus. 

 During the late telophase of the second mitosis in the microspore 

 mother-cell, a readjustment of the spindle-fibers occurs giving 

 rise to the complex figure that has been described as character- 

 istic of spore-formation in many plants. The development of 

 the archoplasmic structures connecting the nuclei of the tetrad 

 is much less marked than in Podaphyllwn (Mottier '97) and in 

 many other phanerogams (fig. 44). By the time the nuclei 

 have reached the resting stage, a division has occurred in the 

 cytoplasm giving rise to four cells which are surrounded by 

 delicate clear walls. A prominent thickening of the wall of the 

 spore-mother-cell takes place, and at the same time a thick wall, 

 continuous with the inner portion of the mother-wall, appears 

 between the daughter-cells. 



This wall frequently attains remarkable thickness. Whether 

 it constitutes an inner wall, or is merely a thickening of the 

 primary wall by the deposition of new material on its inner sur- 

 face, I am unable to say. The outer, primary wall stains more 

 deeply and is frequently seen separated from the inner broad 

 portion (figs. 44-47). This inner wall, which is continuous with 

 the broad walls separating the young microspores, stains deep 

 yellow with orange G, if the orange is allowed to act from 

 one to two minutes ; it appears a pale rose when treated with 

 safranin, but fails altogether to stain with iron-hasmatoxylin. 

 In a few instances, slight evidences of stratification have been 

 observed, but ordinarily the wall appears perfectly homogene- 

 ous, giving the impression of a liquid or viscid substance in 

 which the spores are imbedded ; but the fact that it is often 

 separated from the outer wall by a clear space, and also that it 

 is left behind as a definitely outlined wall after the escape of 

 the spores militates against the probability of its fluid nature. 

 After the spores have grown for a certain period the mother- 

 wall is ruptured and the spores are liberated. At this time the 

 empty mother-cell with its four chambers is often met with 

 (figs. 48, 49). 



In so far as I am aware, this permanent division of the 

 mother-cell into four compartments by thick cellulose walls has 



