114 



ormoci ,oss \i i s 



of the original sporangiogenic bands. Bowei thinks that .ill of the sporogenous 



tissue can not be traced back to a single primary archesporial cell, and that spore- 

 bearing tissue is formed secondarily In periclinal divisions in the cells outside 

 of the original archesporium. In some of the very young sporangiophores of 0. 

 pendulum there can sometimes be seen a single large epidermal cell which may 

 possibly be the mother cell of a young sporangium, bur it is ven difficult to determine 

 this point satisfactorily. 



After the archesporium is differentiated there is a rapid division in its cells and 

 there is thus formed a very large mass of cells, whose limits, however, are not always 

 very clearly marked. Later on the contents of these cells become denser and are 

 more easily distinguished from the surrounding sterile tissue. 



The cells King outside the archesporium divide rapidly both by longitudinal 

 and transverse walls anil give rise to the thick outer wall of the sporangium. In lon- 

 gitudinal sections through the sporangium two rows of cells may he seen extending 

 from the mass of archesporial cells to the outside of the sporangium. These two 

 rows of cells mark the point where the transverse cleft arises by which the spo- 

 rangium opens at maturity. The outercells derived from the archesporial complex 



Fig. 85. 



A, B. Young sporangia; C, an older sporangium of Bolr\chium virgtnianum. In C, the sporogenou 

 tissue is shaded; the nucleated cells adjoining form the tapelum. 



do not develop into spores, but constitute the tapetum, which later becomes dis- 

 organized and forms a sort of plasmodium extending among the growing spore 

 mother cells, and is, no doubt, of great importance in the further development of 

 these. Bower thought that some of the inner cells of the archesporial tissue contrib- 

 uted to this plasmodium, but a further study has led him to the conclusion that this 

 is not the case and that all of the inner cells of the archesporium develop into spores. 

 This view is confirmed by the recent paper of Burlingame ( Burlingame I ), who 

 investigated the development of the spores in 0- reticulatum. 



At maturity the sporangium opens by a transverse cleft whose position is already 

 evident in the younger stages of the sporangium. As the cells shrink with the drying 

 of the ripe sporangium the spores are crowded out through this cleft, hut there is 

 no special mechanism like the annulus found in the sporangia of the higher ferns 

 which facilitate the dispersal of the spores. 



Our knowledge of the development of tin sporangium of Botrychium has been 

 based largely upon the study of B. lunaria. I have investigated with some care the 

 development in B. virginianum, which differs mainly from B. lunaria in the smallei 



