LIFE HISTORY OF PINUS 75 



The state of disintegration referred to above is always con- 

 fined to the upper of the two daughter-cells and never occurs in 

 the lower one, except in those cases in which the whole ovule 

 is undergoing destruction. The lower cell invariably divides 

 again and the basal cell thus formed constitutes, in every instance 

 observed, the functional macrospore. The lack of constancy 

 in the division of the upper cell would naturally give rise to 

 some axial rows of four cells and some of three, and this is 

 exactly what we find (figs. 144, 145, plate XIV). Fig. 143 shows 

 the second division of the lower cell just completed, and it is evi- 

 dent from the structure and appearance of the uppermost nucleus 

 that it would never have divided. In the axial row presented in 

 fig. 144 some time has elapsed since the mitosis was completed, 

 as evidenced by the increase in size of the lowest cell of the row. 

 The upper of the two cells formed as a result of the first mitosis 

 still remains undivided, and, moreover, it would not have divided 

 later, judging both from its appearance and from the fact that the 

 rapid growth of the initial cell of the female gametophyte would 

 soon have been instrumental in effecting its obliteration. Juel 

 ('00) finds that these cells do not divide simultaneously in Larix^ 

 but he does not find the division completed in the lower cell before 

 it begins in the upper one. In the single preparation showing 

 the second division in the macrospore-mother-cell, both nuclei 

 are dividing, and both are in the same stage of the prophase, 

 but this does not necessarily mean that when both cells divide 

 they always do so synchronously. This lack of uniformity in 

 the number of cells in the axial row is not peculiar to Pinus ; 

 it has been observed by many investigators in a large number 

 of plants including both Gymnosperms and Angiosperms. 



Coulter and Chamberlain ('01) figure an axial row of four 

 cells in Piniis Laricio, and, as above indicated, such an axial 

 row is frequently met with in the species of pines which I have 

 studied, but it is much more common in Piniis ausiriaca than 

 in the other species (figs. 145, plate XIV, 142, plate XIII, and 

 261, plate XXIII). There is no doubt whatever, after a study of 

 many preparations showing the axial row, that in the great 

 majority of cases in Pinus Strobus and P. rigida the upper cell 

 remains undivided and that the usual axial row in these species 



