LECTURE XVII. 



ASEXUAL reproduction by gemmae in Marchantia usually takes 

 place in the autumn and spring, while sexual reproduction is 

 commonly observed during the summer. Hence it is that the 

 sexual organs are not commonly found on the plants with most 

 cupules. Plants in the sexual stage are very easily recognised. 

 They are furnished with very remarkable vertical branches. 

 These branches are of two kinds, antheridiophores and arche- 

 goniophores. Both kinds seem never to occur on the same plant. 

 They are developed at the growing region and form a direct con- 

 tinuation of the mid-rib ; but they bend vertically upwards, using 

 an indentation at the end of the horizontal branch to emerge 

 from underneath the margin of the thallus. The margin of the 

 thallus often by subsequent growth closes round them so that to 

 casual observation they appear as growing up through the thallus. 

 The antheridiophore has a whitish stalk about 1-3 cm. long, 

 which supports a disc-shaped top. The stalk is roughly prismatic, 

 having five faces. Two of these faces are bowed outwards and 

 three are grooved. The grooves on two are very deep and the 

 sides close over them, so that two vertical tubular channels are 

 formed running down the length of the stalk. At the upper end 

 the stalk spreads out to form the disc. Eight distinct lobes on the 

 margin of the disc show that we have to do with a system of 

 branches, each lobe representing the apex of a branch. The 

 middle of the disc is thick and massive and the margin is mem- 

 branous. Its surface resembles the upper surface of the thallus 

 and is provided with numerous air-chambers, each with its central 

 pore. In addition to these pores the upper surface of the disc 

 is studded over with many dark purple spots which are most 

 numerous along the low ridges which run radially out to the lobes 

 of the margin. These spots indicate the openings of narrow 

 canals leading down into deep rounded cavities in the antheridio- 

 phore. The cavities are lined by a layer of cells, the walls of 

 which are coloured a deep purple. Each cavity is almost com- 

 pletely filled with an egg-shaped body the antheridium attached 



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