ii8 



MORPHOLOGY OF GYMNOSPERMS 



ened, and the layers between the epidermis and the spores disorganize, 

 as in the sporangia of ferns. Two rows of elongated thin-walled 



cells bordered by cells with 

 thick walls give the de- 

 hiscence much the appear- 

 ance of that of Angiopteris. 

 The formation of micro- 

 spores from the mother cell 

 has been described by 

 JuRANYi (5) and by Miss F. 

 Grace Smith (56) for 

 Ceratozamia, and by Treub 

 (11) for Zaniia muricata. 

 With the appearance of the 

 cell plate in the first divi- 

 sion, a ringlike thickening 

 of cellulose appears on the 

 wall of the mother cell, and 

 proceeding from this ring a 

 thick wall develops between 

 the two daughter cells. 

 Each of these two cells 

 divides and heavy walls are 

 formed again, and within 

 this heavy four-celled and 

 often lobed case the micro- 

 spores are organized. The 

 number of chromosomes in 

 the pollen mother cells of 

 Ceratozamia and Zamia is 

 12; other numbers (7, 17) 

 have been reported for 

 Ceratozamia, but technic 

 at that time was hardly 

 adequate to meet the trying 

 demands of such difficult nuclei. Miss F. Grace Smith counted 50 

 cases in Ceratozamia, and in forty-six found 12 chromosomes, in three 



103 



Figs. 101-104. — Zamia floridana: earh- 

 stages in the development of the microsporan- 

 gium; fig. loi, single hvpodermal archesporial 

 cell; fig. 102, first periclinal division; fig. 103, 

 usual divisions following stage shown in 

 previous figure; fig. 104, longitudinal section 

 of a sporangium in a more advanced stage; all 

 figures X920. — After V. Grace Smith (56). 



