260 



not only are the sexual organs mature, but fecundation has been 

 effected and the first division of the embryo completed. 



As was the case with pretty much all of the higher crypto- 

 gams, Hofmcister was the first to make extended observations m 

 regard to the life-history of this group; but as was generally the 

 case, while his investigations were in some particulars correct 

 enough, the details were often very erroneous, owing largely, no 



doubt, to imperfect methods. 



Hanstein* studied in detail the development of various species 



of Marsilia, but owing to his method of treating the young 



prothallia, made very serious mistakes. Through the action of 

 caustic potashj which he employed freely in order to render the 

 prothallia transparent, the young cell-walls are so much swollen 

 and dissolved as to be practically invisible, and this led him to 

 believe that the female prothaUium was at first composed of 

 primordial cells which later became surrounded with membranes, 

 and that the contents of the microspore divided at once into 

 thirty-two primordial cells, the mother-cells of the spermatozoids. 

 Archangell,t some ten years later, made Pihdaria the subject 

 of special study and found that the cell-division in the female 

 prothallium was effected by means of walls, and also demonstrated 

 the presence of a vegetative cell in the male prothallium. The 

 latter fact was also established by Sadebeckf for Marsilia, 



By means of more improved microscopic methods it is possible 

 to obtain thin sections of the youngest stages of the female pro- 

 thallium of both Piliilaria and Marsilia, and these show an almost 

 identical structure. The plasma of the upper part of the spore, 

 becomes cut off by a transverse septum from the cavity of the 

 spore, and from this upper cell is produced by repeated division 

 a single archegonlum, all the divisions being effected by cell- 

 walls. The archegonium is of the same type as in other pterido- 

 phytes, but has a very short neck, especially in Marsilia, 



The microspores divide first into two cells, a small basal cell, 

 (the vegetative part of the prothallium) and a much larger one, 

 the mother-cell of the antheridium. The basal cell in Pihilaria 

 often divides again into two cells of unequal size. The antheri- 



1. c. 1 1- c. 



f Schenck's Handbuch. 



