82 MARGARET C. FERGUSON 



conception of the embryo-sac seems to the writer to form a more 

 satisfactory basis for a rational explanation of the structure, or 

 composition, and homologies of the embryo-sac than do any of 

 the existing theories regarding the nature of this body. 



CHAPTER IV. 



The Female Gametophyte. 

 development of the prothallium. 



The First Period of Growth. — We are indebted to Hof- 

 meister ('51) for our first definite knowledge regarding the life 

 history of the female gametophyte in the Gymnosperms. It is 

 true some errors in observations were made, but they were inter- 

 mingled with much that has stood the test of the most modern 

 research. In 1879 Strasburger declared the " transitory endo- 

 sperm " described by Hofmeister to be a fallacy, but he himself 

 fell into quite as grave an error, though in the opposite direction, 

 when he stated that the primary nucleus of the embryo-sac 

 remained undivided during the first year, an observation since 

 corrected by himself. 



As already stated, the young macrospore immediately organ- 

 izes a peripheral layer of cytoplasm and passes through a period 

 of growth which continues for six weeks or more. The degree 

 of development which has been attained by P. austriaca 

 on June 13, 1898, is shown in figs. 145 and 147 ; the first 

 division of the macrospore-nucleus in this species occurred 

 on July 29 of the same year, as illustrated in figs. 149 and 150. 

 The germinating macrospore had now enlarged to such an 

 extent that it was found necessary to reduce the scale of mag- 

 nification at this point so that a comparison of the figures does 

 not present, visually, the amount of growth which ensues 

 between the organization of the macrospore and its first division. 

 Pinus differs substantially in respect to the very marked growth 

 of the macrospore before the first division of its nucleus from 

 Larix where two nuclei are formed before there is any con- 

 siderable increase in size of this cell (Juel ('00) plate xv, figs. 



