36 HUMPHREY 



ciete produce spores of similar character. Goebel,' however, 



suggests that localities favorable to Corsinia may not always be 



moist, and in the case of the aquatic Riccie^e the perinium very 



effectively serves as a protection against invasion of the spore by 



fungal hyphas. 



Although the great majority of our xerophilous liverworts 



produce thick-walled spores there are such exceptions as Po7'- 



ella bolanderi 2iV\di Radiila complanata whose spores are protected 



by a thin, frail exosporium and are incapable of withstanding 



prolonged drying. These liverworts grow on tree trunks or 



exposed surfaces of rocks where they are subject to sudden 



drying out and we should naturally expect their spores to be 

 better protected. 



The character of the spore-w^all, however, might suggest the 

 possibility of these forms being naturally more h3'^grophilous in 

 character, while their adaptation to a dry habitat is merely one 

 phase of the extreme adaptability common to both forms. 



In order to get at the relationship of the exospore to the spore 

 a study of the life conditions of the several species is necessary 

 and some light will be thrown upon the subject w^hen we ascer- 

 tain at what time, in nature, the spores of a large variety of 

 forms germinate. With a large number of forms it has been 

 repeatedly shown that spores sown on soil under conditions as 

 nearly normal as possible germinate only after a long period of 

 rest. 



In June, 1904, the writer sowed on sterilized earth, a quantity 

 of spores of Fossombi'onia that had been gathered a few days 

 before sowing. The culture was made in an earthen saucer 

 and placed within another close-fitting earthen saucer, in which 

 was maintained a supply of water so that the dirt was kept con- 

 stantly moist from below. The culture was placed on a table 

 near a window where it could receive a nearly normal supply 

 of light. During the latter part of August a few spores had 

 germinated but not until October did they germinate in any 

 great number. The spore of Fossombronia, while perhaps not 

 as well protected as that of Finibriaria or Targionra^ nevertheless 

 is furnished with a resistant exosporium and is well adapted to 



' Loc. cit., 107. 



