LIFE HISTORY OF PINUS 9! 



of June, the time varying somewhat with the species and with 

 the season. The degree of development which the prothallium 

 has attained when the archegonia-initials make their appear- 

 ance also varies not only in the different species but in the same 

 species. The differentiation of the archegonia may be deferred 

 until the prothallial cells have united to form a continuous tis- 

 sue ; but it quite as frequently happens that, while there still 

 remains a comparatively large, open space at the center of the 

 prothallial cavity, certain cells at the micropylar end of the pro- 

 thallium divide by periclinal walls more rapidly than do the other 

 cells of the endosperm and become comparatively rich in cyto- 

 plasm ; several of the superficial cells in this region do not so 

 divide, but continue to grow, and are distinguished from the 

 adjacent cells by their greater size, larger nuclei and more 

 vacuolate cytoplasm. These are the initial cells of the arche- 

 gonia (fig. 162, plate XV, and 169-171, plate XVI). 



In less than a week after an archegonium-rudiment has ap- 

 peared, and while it is still quite inconspicuous, it divides, giving 

 rise to a small upper cell, the mother-cell of the neck, and a 

 large, lower cell which forms the venter of the archegonium 

 (figs. 171, 172, plate XVI). The small cell immediately divides 

 by an anticlinal wall, and the two cells thus formed divide by 

 walls that are perpendicular to the first, the resulting four cells 

 all lying in the same plane. These constitute what may be called 

 the normal neck in Pinus Strobus (figs. 173, 177, 180). Con- 

 siderable irregularity in the number and arrangement of the 

 neck-cells has, however, been noted even within the same spe- 

 cies. Frequently two of the four cells divide again, as figured 

 by Strasburger for Pinus Strobus in 1869, the six cells being 

 arranged in a single layer (figs. 178, 183, plate XVI, and 212, 

 plate XIX). Occasionally all four cells divide by anticlinal 

 walls, the neck then consisting of eight cells, all of which lie in 

 the same plane (figs. 179, plate XVI, and 213, plate XIX). In 

 rare instances the four cells divide by periclinal walls, when the 

 eight cells which compose the neck of the archegonium are dis- 

 posed in two tiers of four cells each (fig. 187, plate XVII). 

 This last represents the structure of the neck in Pinus sylvcstris 

 as figured by Mottier ('92) and Blackman ('98), and it is evi- 



