METHODS 25 



than in that species. The best differentiation was secured by Haiden- 

 hain's iron-alum-haematoxylin. The blepharoplasts could not be made 

 out, but presumably are present. 



A sufficient study of the spermatogenesis in P. Levieri was made to 

 show that it is very much like that in the other two species. Fig. 12, S, 

 shows the pair of spermatocytes with the separating membrane and the 

 blepharoplasts. The spermatocytes are somewhat larger than correspond- 

 ing stages in P. Zollingeri, measuring about g\i in length. 



The Archegonium 



In all species of Pallavicinia the archegonia are in groups sur- 

 rounded, as already stated, by a double envelope : an outer one, tne invo- 

 lucre, much the more conspicuous before the fertilization of an archego- 

 nium ; and an inner one, which is very small at first, but which after an 

 embryo is formed grows rapidly and forms a conspicuous tubular sheath 

 enclosing the developing sporophyte. 



In P. Zollingeri, the involucre is cup-shaped, with a lobed margin 

 (Fig. 6, G, H). Within this, and surrounding the base of the archegonial 

 group, is the young perianth, which at this stage does not reach above 

 the level of the venter of the archegonia (Fig. 13) . P. radiculosa (Fig. 13, 

 A,B, E) differs from P. Zollingeri mainly in the much greater number of 

 archegonia in the receptacle, and in the more flaring and deeply fringed 

 involucre. P. Levieri is somewhat intermediate in character, both as to 

 the number of archegonia and the form of the involucre (Fig. 13, D). 



The receptacle is at first level with the surface of the thallus, but as 

 new archegonia develop it becomes raised and forms a more or less prom- 

 inent elevation, or placenta, to which the archegonia are attached (Fig. 

 13. E). 



Of the three species examined, P. radiculosa was the best for the 

 study of the archegonium, as all stages of development were present in 

 the material. P. Levieri also showed most of the stages, but as it differed 

 very little from P. radiculosa an exhaustive study was not made. None of 

 the specimens of P. Zollingeri showed very young archegonia, but to 

 judge from the few immature archegonia that were seen it does not differ 

 essentially from the other species. 



Pallavicinia radiculosa, while agreeing in the main with other ana- 

 crogynous Jungermanniales, in the development of the archegonium 

 shows certain differences that may be noted. 



The youngest archegonia (Fig. 14, A, C) show a stalk composed of 

 two or three cells, and a terminal, approximately hemispherical cell from 



