98 



THE BIOLOGY OF A PLANT. 



cell to which the "neck-" aud "canal-cells" are merely acces- 

 sory. 



Fertilization or Impregnation. Fertilization, or the sexual act, 



is performed as follows : Spermato- 

 zoids in vast numbers are attracted 

 to the mouths of the archegonia and 

 there become entangled in the mu- 

 cilage (Fig. 66). In favorable cases 

 one or more work their way down 

 the mucilaginous canal, and at length 

 one penetrates and fuses with the 

 oosphere. 



It is known that one spermatozoid is 

 FIG. 66. (After strasburger.) Mouth of enough to fertilize the oosphere, and 

 an archegonium of pteris semdata, pro bably one only penetrates it; but sev- 



crowded with spermatozoids striving 



to effect an entrance. era l are often seen in the mucilaginous 



canal. It has recently been shown that 



the mucilage contains a small amount (about 0.3$) of malic acid, which 

 probably acts both as an attraction to the spermatozoids and as a stimulus 

 to their movements. Pfeffer has shown that capillary tubes containing a 

 trace of a malate in solution are as attractive to the spermatozoids as the 



mucilage in the central canal. 



The entrance of the spermatozoid into the ovum and its 

 fusion with it 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 oaspore. 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 oopJiore (p. 89). 



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

 sporophore (p. 89), now rapidly becomes multicellular by dividing 

 first into hemispheres, then into quadrants, etc. (Fig. 68 ; com- 

 pare Fig. 21). The first plane of division is approximately a 

 prolongation of the long axis of the archegonium (Fig. 68). 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 lower 

 anterior quadrant as it undergoes further division grows out 

 into the first root; the upper anterior quadrant in like man- 



