288 Trans. Acad. Sci. of St. Louis. 



one case I found spermatozoids attracted toward and actually 

 entering six archegonia. There is usually but one or at most 

 two fully developed archegonia at any one time except in 

 these older and larger forms. I have sectioned some hundreds 

 of prothallia and found but one case where an archegonium 

 was developed on the upper side. The case occurred where 

 the prothallium producing it was overlaid by another so that 

 its presence was due to the conditions of moisture and nour- 

 ishment induced by the second prothallium, agreeing with the 

 result of experiment where such archegonia were artificially 

 induced by Heinricher. 



If, however, we turn to Woodsia ohtusa and consider the 

 prothallium in that fern for comparison, we do not find the 

 regularity in shape and form so distinctive of the others. 

 The prothallia here tend to grow in length with approxi- 

 mately a regular width. The sides are sinuate so that such 

 prothallia do not usually lie flat upon the substratum. Here 

 as in the others the margin of the prothallium is but one cell- 

 layer in thickness, but instead of a gradual thickening we 

 find a definite thickened ridge developed on the under side 

 upon which antheridia and archegonia are produced. The 

 production of sex organs begins somewhat earlier in this form, 

 and continues in the newer portion of the gradually length- 

 ening prothallium until a fertilization is accomplished. 



In contrast to the observations of Jeffrey on Botrychium, 

 I found but one case among the large number examined where 

 two archegonia upon the same prothallium had been fertil- 

 ized, and produced embryos. In this case (fig. 49) the two 

 embryos formed lie so close together as to indicate a possibil- 

 ity of the ultimate fusion of the two had their development 

 been continued. This observation is of interest on account of 

 its bearing upon the views of polyspermy in ferns, advanced 

 by Lowe ('95) in his "Fern Growing," where he finds on 

 different portions of the same plant the characters of as many 

 as three or even six ( !) different species. He has not at- 

 tempted to determine by histological methods whether this 

 remarkable phenomenon results from the fertilization of three 

 or more separate oospheres by spermatozoids of as many dif- 

 ferent species, and a later fusion of the embryos into a sort 



