§2 



MOSSES AND FERNS 



CHAP. 



older plant. Leitgeb (Fig. 17, PI. IX.) shows a condition 

 that looks as if at an earlier stage a two-sided apical cell had 

 been present, but he says nothing in regard to this. The 

 sexual organs appear while the plant is extremely small. Leit- 

 geb says he observed the first indications of them on individ- 

 uals only one millimetre in diameter, and before the first papil- 

 late hair on the ventral surface had been formed. 



In the commonest Californian species, ^. cristatus the 

 spores separate completely at maturity. The early stages of 

 germination are like those in S. terrestris. There is usually 

 a two-sided apical cell at first, which later is replaced by the 

 type found in the adult thallus. 



^^yi\wi^ 



Fig. 34. — Geoihallus tuberosus. A, Male plant, X15; B, section of female plant, X15; 



/. young tuber. 



Where there is an excess of moisture the thallus may be- 

 come much larger than usual, this being especially noticeable 

 in the male plants. There is often, under these conditions, 

 a development of leaf-like marginal lobes. This excessive 

 vegetative development of the thallus is accompanied by a 

 marked diminution in the number of the sexual organs. 

 (Campbell (17)). 



Geothallus. 



Evidently closely allied to Sphcerocarpus is a remarkable 

 Liverwort, as yet found only near San Diego, in Southern 



