J 



Graham : Conocephalum conicum . 621 



side the closed mouth of the archegonial cavity is pushed around 

 toward the outside of the gametophore {^figures 4.0, 45). Fur- 

 ther growth of the sporogonium and calyptra is accompanied by 

 still further development of the tissue separating the air-chambers 

 adjacent to the stalk, so that at maturity the closed opening is 

 found nearly opposite the foot of the sporogonium on the outer side 

 of the gametophore {^figure 4^. The whole outer enveloping 

 sheath is therefore formed by the elongation of the laminae or 

 plates of cells separating the air-chambers in the wall o{ the arche- 

 gonial cavity adjacent to the stalk of the gametophore. 



At the time the sporogonium has reached the stage of devel- 

 opment shown in figure -/j, and at the time when the spore 

 mother-cells have separated from one another, it may be observed 

 that its growth has not kept pace with that of the calyptra or the 



w 



enveloping sheath, so that a considerable space appears between 

 the wall of the sporogonium and the surrounding calyptra. The 

 calyptra and sheath, having no support from within, are infolded 

 or collapsed into this depression. As further development takes 

 place the sporogonium comes to fill this space so that the envel- 

 oping calyptra and sheath are tightly stretched about the distal 

 end of the sporogonium {^figures ;^§, ^/). 



That the calyptra and sheath do not form one continuous tis- 

 sue is clearly shown by the fact that the shriveled neck of the old 

 archegonium is found lying between these two envelopes, some- 

 times closely squeezed between them {^figures j^^ j§^ ^o ^/, jo). 

 That the outer sheath is made up of plates of cells representing 

 the boundaries between air-chambers is clearly shown in figures 



34^^ 35j 4^i 43f 4p, and 5/. An examination of these figures 

 shows that the tissue of the calyptra is composed of cells closely 

 united while the outer sheath is composed, in longitudinal section, 

 of several rows of cells entirely separated from one another [fig- 

 ures j^, J5, ^/). It should be mentioned that the apparent con- 

 tinuity of the cell walls of the different plates of the sheath, shown 

 in figures ^5?, 50, and j/, is due to the overlapping of the cells, 

 because the sections are cut in a slightly oblique direction. The 

 true condition is, however, perfectly apparent in figures j^, J5, 

 41, 43, and 45. 



This outer sheath formed from the tissues of the gametophore 



