EXPLANATION OF PLATES. 



PLATE 4. 



A spore of Onoclea slrulhiopteris from wliicli tlie exospore has been removed, X 150. 



A similar spore Ijegiuiiing to germinate Ijy tlie splitting of the middle coat and the protrusion of the en- 



dospore. 

 Spore in whicli the first root-hair, ?•, is separated from the body of the spore; the exospore is present, 



X 150. 

 Later stages in which the body of the spore has divided to form the body of the young prothallium. lu 



5, the second root hair, r', is forming, X 150. 

 Successive steps in the formation and division of the apical cell, o, of the prothallium, X 150. 

 Showing the way In which the apical cell, a, is obliterated, X 150. 

 Young female prothallium, one month from the time of germination, X 150. 

 Young male prothallium with antheridia, -'an," X 125. 



Small male prothallium, consisting of but one row of cells, an, antheridium, X 1,">0. 

 Formation of the division walls in the antheridium, X 500. For the sake of clearness the contents of tlie 



cells are omitted. 

 Formation of the mother-cells of the antherozoids. In optical longitudinal section, X 500. 

 First divisions of the central cell of the antheridium seen from above, X 500. 

 Kipe antheridium, X 500. 



Successive stages in the formation of the antherozoids, X 625. 



Antherozoids escaped from the antheridium, but still enclosed in a thin membrane, X C35. 

 Complete antherozoids. v, vesicle containing granules, X 625. 

 Antheridium provided with a pedicel, P, X 150. 

 Early stages in the development of the arcliegonium, X 500. 



PLATE 5. 



Figs. 1-5. Early stages in the development of the archegonium, X 500. m, mother-cell of the archegouium; b, 

 bas.al cell; c, central cell; ne, neck cell; ca, canal cell of the neck. Figure 1 is viewed from above, 

 the others from the side. 

 " 6-7. Later stages in the development of the archegonium, X 500. o, the germ-ceU; m, mass of protoplasm and 

 mucilage formed from the canal cell. In figure 6 the contents of canal-cell have collected in three 

 masses ; Fig. 7, Ripe archegonium, opening and discharging the contents of the neck. 

 Fig. 8. Central cell and germ-cell of a ripe archegouium. )•, receptive spot ; o, germ-cell, X 500. 



" 9. Antherozoids entering an archegouium, X 500. 



" 10. Germ-ceU, twenty-four hours after fertilization, X 500. 



Figs. 11-16. Successive stages in the development of the embryo, in optical longitudinal section. Fig. 15, two-celled 

 emljryo; the nucleus of one-half has divided again ; Fig. 11, four-celled embryo ; Figs. 12-14, more 

 advanced stages. All magnified live hundred diameters; Fig. 15, X 150. In all cases the section was 

 perpendicular to tlie surface of tlie prothallium. Z, leaf; r, root; s(, stem ;/, foot. The heavy lines 

 mark the primary division walls of the embryo. 

 " 17-20. Young embryos, seen in optical longitudinal section, the section being parallel to the surface of the pro- 

 thallium. Fig. 17, four-celled; Fig. 18, eight-celled; Figs. 19, 20, older embryos. All magnified 

 five hundred diameters. 



PLATE 6. 



Fig- 1. Emlwyo seen in optical longitudinal section, the section parallel to the surface of the prothallium, X 



500. I, leaf; r, root. 



" 2. An embryo ready to brealc through the prothallium, X 150. Longitudinal section perpendicular to sur- 



face of prothallium. I, leaf; r, root; st, stem;/, foot; pr, prothallium; ar, neck of the archegonium. 



" 3. A similar section through the leaf of a somewhat older embryo thau 1, showing the bifurcation of the 



apical cell, a a', the two new apical cells. 



" 4. Koot of the same embryo, X 245. a, apical cell. 



" 5. Young plant with the first leaf and root complete, X 3. pr, prothallium. 



" 6. Young fourth frond, showing the division of the apical cell, X 245. 



(61) 



