FERTILIZATION AND DEVELOPMENT. 



139 



proximal end. The oosphere is the all-important female germ-cell to which 

 the " neck-" and " canal-cells " are merely accessory. 



Fertilization or Impregnation. Fertilization, or the sexual 

 act, is performed as follows : Sper- 

 matozoids in vast numbers are at- 

 tracted to the mouths of the arclie- 

 gonia and there become entangled 

 in the mucilage (Fig. 78). In 

 favorable cases one or more work 

 their way down the mucilaginous 

 canal, and at length one penetrates 

 and fuses with the oosphere. 



FIG. 78. (After Strasburger.) 

 Mouth of an archegonium of Pte- 

 ris semtlata, crowded with sper 

 matozoids striving to effect an en- 

 trance. 



It is known that one spermatozoid is 

 enough to fertilize the oosphere, and 

 probably one only penetrates it ; but sev- 

 eral are often seen in the mucilaginous 

 canal. It has been shown that the muci- 

 lage contains a small amount (about 0.3?) 

 of malic acid, which probably acts both as an attraction to the spermato- 

 zoids and as a stimulus to their movements. Pfeffer has proved that 

 capillary tubes containing a trace of a malate in solution are as attractive 

 to the spermatozoids as is the mucilage in the central canal, and phe- 

 nomena of this kind (chemiotaxis) have recently been shown to be common 

 and highly important. 



The entrance of the spermatozoid into the ovum and its 

 fusion with if- mark an important epoch in the life-history of the 

 fern. The oosphere is from this instant a new and very differ- 

 ent thing, viz., an embryo, and is known as the oospore. It is 

 now the first stage of the asexual generation, though it is still 

 maintained for some time at the expense of the sexual generation 

 or oophore (p. 130). 



Growth of the Embryo. The oospore, or one-celled embryonic 

 sporophore (p. 130), now rapidly becomes multicellular by di- 

 viding first into hemispheres, then into quadrants, etc. (Fig. 80 ; 

 compare Fig. 14). The first plane of division is approximately 

 a prolongation of the long axis of the archegonium (Fig. 80). 

 The second is nearly at right angles to it, so that the quadrants 

 may be described as anterior and posterior to the first plane. 

 The fate of the quadrant-cells is of special importance. The 



