CONIFERALES (PINACEAE) 



261 



extremities of the sac, so that when wall-formation occurs three dis- 

 tinct parietal regions are apparent (upper, middle, and lower), the 

 ends of the sac becoming filled with compact tissue while the middle 

 region is hardly beyond the stage of free nuclei. In filling up the 

 center of the sac with tissue, the belated middle region grows cen- 

 tripetally, its inner cells being open toward the center of the sac, as 



286 



287 



Figs. 285-288. — Cryptomeria japonica: development of the endosperm; fig. 285, 

 longitudinal section of upper portion of endosperm showing multinucleate condition 

 and also that the walls are incomplete; May 26, 1902; X235; fig. 286, telophase of 

 the mitosis which is to result in the formation of a binucleate cell hke those shown in 

 fig. 288; May 29, 1903; X 1,000; fig. 287, a later stage in the same mitosis, the two 

 daughter nuclei completely inclosed by the kinoplasmic fibrils; X 1,000; fig. 288, 

 portion of the endosperm soon after free cell-formation; the membrane formed by 

 the kinoplasmic fibrils has inclosed both daughter nuclei; the free cells crowded 

 together resemble a tissue; May 29, 1903; X 320.— After Lawson (93). 



usual. The details of this centripetal growth, as given by Arxoldi, 

 are that when the centripetally growing walls have reached the center 

 and the end walls have been formed, the result is a series of radially 

 elongated cells, which he calls "alveoli." In these cells nuclear 

 division with wall-formation occurs, so that each alveolus becomes 

 divided into several cells. In investigating Sequoia gigantea, the 

 same investigator (64) discovered that the endosperm development 

 is uniform, and with no such regional differences and cell-formation 

 by alveoli as are exhibited by its fellow species. Lawson's account 



