152 FUNDAMENTALS OF CYTOLOGY 



matured eggs are in the vicinity, the sperms tend to move toward them 

 along a maUc acid gradient. Many sperms may enter an archegoniimi, 

 l)iit ordinarily only one unites with the egg. The fate of the components 

 of the sperm in syngamj^ is apparently not precisely the same in all 

 ferns, but in general their behavior is as follows. The cytoplasmic 

 vesicle is lost by the swimming sperm before it reaches the egg. The 

 other components enter the egg cytoplasm, although the cilia have been 

 reported in at least one species to remain outside. The nucleus then 

 separates from most or all of the other components (residual cytoplasm 

 and portions of the motor apparatus) and alone imites with the egg 

 nucleus. 



The fertilized egg develops into an embryo sporophyte, the early stages 

 being passed through entirely within the archegonium. In ordinary 



anth 



B 



Fig. 111. — A, apogainy in a fern: young sporopliytic tissue (s) developing directly fi'om 

 gametophytie tissue (g). (After Farmer and Dighy.) B, apospory in a fern: gametophyte 

 with antheridiuin arising directly from sporophytic tissue at base of sorus. sp, sporangia, 

 r, rhizoid. {After F. 0. Bower.) 



ferns the planes of the first few divisions in the spherical cell form a 

 i-egular geometrical pattern: hemispheres, quadrants, and octants are 

 formed in order. The embiyonic parts — stem, root, leaf, and absorbing 

 foot — differentiate in regular positions with respect to the early sub- 

 divisions. In some ferns a considerable mass of embryonic tissue is 

 formed before a gradual differentiation of parts becomes visible. Thus 

 it appears that in plants, as in animals (page 129), cleavage and embryonic 

 differentiation may be variously related in time and that the numerical 

 equalit}' of quadrants and embryonic parts in some ferns with early 

 differentiation does not mean that the cleavage divisions determine the 

 differentiation of these parts. 



The ferns have long been favorite objects for the study of apogamy 

 and apospory (Fig. 111). These aberrations in the reproductive process 

 have been found to occur more or less constantly in several genera, and 

 they have been induced by cultural conditions in certain others. In 

 apogamy the meristematic region of the gametophyte gradually produces 

 a young sporophyte directly, gametes being in no way concerned. In 

 apospory the meristematic tissue at the leaf margin or the base of a sorus 



