38 STRUCTURE AND LIFE-HISTORY OF HAY-SCENTED FERN. 



The remains of unsuccessful sperms are left after fecundation as a deeply- 

 staining- cap over the top of the egg-cell. The fertilized egg rounds off 

 and comes to rest, with a large central nucleus and nucleolus (fig. 224). 



About half of the mature prothalli, with apparently perfect archegonia, 

 will actually be fertilized when mounted on a slide with mature males. In 

 such cases not only is the receptive archegonium filled with sperms, but 

 many older archegonia, up to a dozen on a single plant, including such as 

 are brown with age, are quite as eagerly crowded into by numbers of 

 sperms. Only once, however, have I known two embryos to appear on 

 one prothallus. Young archegonia continue to develop on the fertile 

 prothallus for a time. But after the embryo is fully established (i.e., 

 octant stage), sexual organs cease to develop. Fertilized eggs were found 

 about 7 days after my cultures had been flooded with water. In 16 days 

 many embryos were visible with a hand-lens. 



THE YOUNG SPOROPHYTE. 



The first cleavage-plane (basal wall) in the fertilized egg includes the 

 axis of the archegonium, and lies transversely to the axis of growth of the 

 prothallus. It divides the egg into anterior and posterior halves (see 

 below). The second (quadrant) wall passes horizontally and at right 

 angles to the axis of the archegonium. In each quadrant, then, a vertical 

 wall is formed at right angles to the two preceding, dividing the embryo 

 into octants. These octant walls do not correspond in the different quad- 

 rants, but the octants are from the first unequal in size (figs. 233, 234). 

 Supposing the prothallus to lie before the observer with cushion down- 

 ward and the notch on the farther side, we may speak of right and left, 

 anterior and posterior, upper and lower portions. The fate of the octants 

 may be stated thus: 



i. Anterior upper right octant=Stem initial 



. . , or -vice versa. 



2. Anterior upper left octant Irregular 



3. Anterior lower right octant = ) 



4. Anterior lower left octant = J F 



5. Posterior upper right octant = [ 



6. Posterior upper left octant = j 



7. Posterior lower right octant=Irregular ) Qr ^^ versa >. 



8. Posterior lower left octant =Root j 



It must not be supposed, however, that this arrangement is invariable. 

 On a prothallus with two embryos one has the root-intitial in octant 8, the 

 other in 7. Octants 2, 3, 5, 7 are smaller than 1, 4, 6, 8. The first 

 division in 2, 4, 6, 8 is parallel to the basal wall and near to it. In 8 

 the succeeding divisions are parallel to the other primary walls, and then 

 to the curved outer wall. The resulting tetrahedral central cell is the 

 root initial. It continues to divide in the way which is characteristic for 

 roots (?. v.) (figs. 235,236). 



