486 EXPLANATION OF THE FIGURES. 



PLATE LVIII. 



SELAGINELXA. DENT1CULA.TA. 

 FIG. 



1. Longitudinal section of an unirapregnated prothallium, eleven months after 



sowing. Several archegonia have been exposed by the section ; in one 



of them the spherical cell produced in the central cell is represented, 



X 250. 

 I 6 . Mouth of an archegonium, seen from above, X 350. 

 l c . Aperture of an archegonium, where the cells are extended upwards in a 



papillate manner ; seen obliquely from above, X 1 50. 



2. Archegonium whose upper cells are still in close connection. The free 



spherical cell is not yet formed in the basal cell, X 600. 



3. An archegonium just impregnated, laid open by a very successful longitu- 



dinal section. The mother-cell of the embryo is divided by a transverse 

 septum. Unfortunately the specimen was spoilt before the drawing was 

 finished. A portion of the cellular tissue of the prothallium has been 

 drawn from recollection. Ineffectual attempts have been made to 

 obtain another similar specimen, x 600. 



4. An impregnated archegonium ; in a longitudinal section, which has exposed 



the archegonium in which the rudiment of the embryo has originated, 

 and also the course of the proembryo which has formed the suspensor. 

 x 200. 



5. A similar preparation in which the apex of the second axis of the embryo — 



which is destined to develope leaves — is turned towards the observer, 

 X 150. 



6. A young embryo detached, with a uni-cellular suspensor (a rare case), 



looking upon the wide side of the second axis, x 500. 



7. 8. Similar preparations seen from the narrow side, X 500. 



9. From the wide side; 10. from the narrow side of the second axis, X 500. 



11. Outlines of a prothallium, in which the embryo lies concealed, which latter 



has already begun to form its cotyledons, X 30. 



12. Longitudinal section of a spore whose embryo has lately broken through 



the prothallium ; its leaves are beginning to turn green. The section 

 has carried away the larger part of one cotyledon, its stipule, and several 

 leaves of the two rudimentary axes of the third degree of the embryo, 

 X 30. 



PLATE LIX. 



1—5. Mother-cells of the pollen of Pinus balsamea, X 300 ; fig. 1, at the end 

 of March ; figs. 2 — 5, in the first half of April. 



6. Pollen-mother-cell of Pinus Larix, divided into six special-mother-cells ; 



beginning of March, x 300. 



7. Pollen-cell of the same Pinus on the 21st March, after treatment with a 



solution of caustic potash. The second nucleus is already formed. 



