OP mo GL OSS A CE^ 



97 



and very rarely branches, and then but shghtly. The apex of this shoot 

 finally appears above ground, develops chlorophyll, becomes lobed, and 

 ceases to grow. When fully developed, the prothallium consists of an 

 axial bundle of elongated cells surrounded by shorter 

 parenchymatous cells ; its upper surface is clothed with 

 rhizoids. Its length sometimes amounts to as much 

 as two inches, though generally it is much shorter ; its 

 breadth is always very small. In Botrychium (Lunaria, 

 >^ Sw.) the prothallium is a minute light brown or yel- 

 lowish white ovoid mass of firm cellular tissue, subter- 

 ranean and destitute of chlorophyll, and producing 

 rhizoids from all sides. In both genera the prothallium 

 is monoecious. 



The arckegones, antherids, and antherozoids do not 

 differ materially in structure from those of Filices. 



Fig. 74. — Longitudinal section of prothallium of Botrychium Lunaria^ 

 showing archegones and antherids (x 50). (After Hofmeister.^ 



Neither archegones nor antherids are limited in their 

 production to any particular part of the prothallium. 

 In Botrychium (Sw.) the antherids are cavities in the 

 tissue chiefly of the upper side of the prothallium, and 

 the archegones are produced in their immediate 

 vicinity; in Ophioglossum (L.) they project slightly above 

 the surface. Before opening to discharge the anthero- 

 zoids, they are covered by a few epidermal layers of 

 cells. The mode of formation of the antherozoids 

 resembles that o/ Marattiaces. Their mother-cells 

 originate from repeated divisions of one or two cells of 

 the inner tissue lying beneath these layers. They are 

 comparatively large, and escape through a narrow open- 

 ing in the layers of cells which originally covered the 

 antherid. The archegone consists, of a venter containing the central 

 cell, and a neck composed of four vertical rows, each consisting of two 

 or more cells, and only slightly projecting above the surface. The 



H 



P'iG. 73. — Botrychittm 

 Lunaria Sw. (nat. 

 size). 



