and its relation to that in the Animal Kingdom. 355 



the contents of the central cell not consumed in nourishing the 

 germinal vesicle, appears to be discharged into the canal of the 

 archegonium. 



Ordinarily, more than one archegonium is fecundated on the 

 same ])rothallium. The earliest processes after fecundation has 

 taken place, are so completely accordant with those in the Ferns, 

 that their description may be passed over. Here, again, the 

 primary axis of the embryo remains undeveloped. On one side of 

 its apex shoots forth the secondary axis of the new plant, soon 

 turning upward and penetrating through the prothallium ; op- 

 posite to it, and breaking through the prothallium below, appears 

 the first adventitious root. 



Rhizocarpe^. — To Nageli* we owe the knowledge of the 

 spermatozoids of these plants. They are developed as simple 

 filaments in minute vesicles (nuclei ?), which are contained, 

 singly (Pilularia) or several together (Salvinia), inside small cells 

 produced during the so-called germination of the microspores; 

 this germination consisting of the bursting of the cuticle and 

 the protrusion of the internal cell in the form of a tube about as 

 long as the spore, inside of which those cells are formed, after- 

 wards to be set free by its bui'sting. In Salvinia the microspores 

 are agglutinated together inside theii' sporangium ; they germi- 

 nate without leaving it, their tubes breaking out through itf. 

 From the isolated cells the spermatozoids themselves emerge at 

 once, without any previous escape of their parent-vesicles from 

 the spore-cell. In their motion and the arrangement of their cilia 

 they exactly resemble the spermatozoids of the Polypodiacesef . 



The same inquirer opened the way to the correct compre- 

 hension of the prothallium, which emerges from the summit of 

 the megaspore, composed of few cells, and remains in connexion 

 with the spore to bear the archegonia there. Our insight into 

 the import of this organ was completed by the investigations of 

 Hofmeister§ and jVIettenius||. 



The archegonia of Pilularia perfectly agree with those of the 

 Equisetacese in the main points of structure. In this, as in the 

 next genus, the prothallium bears only one archegonium. 



In Marsilea there is a little difiierence, since not only the four 



favourably ruptured archegonium. Nova Acta A. C. L. C. xxiv. pt. 1. p. 69 



* Fortpflanz. der Rhizocarpeen. Zeitschr. f. wiss. Bot. Heft iii. & iv. 

 p. 188. Zurich, 1846. 



•f* Milde, Beitr. z. Keim. v. Salvinia u. Pilularia. Nova Acta A. C L. C. 

 xxiii. pt. 2. p. 642. pi. 60. 



X Hofmeister, Vergleich. Untersuch. p. 109. 



§ Op. supra cit. p. 103 ; and Fruchtbild. u. Keim. der hoher. Krvpt. 

 Bot. Zeit. 1849, p. 793. 



II Beitr. z. Botanik, Heft i. p. 3. 



23* 



