No. 435.] ANTITHETIC VERSUS HOMOLOGOUS. 163 



the non-homologous, sexually developed sporophyte of the 

 Bryophyte, is not explained. 



Mr. Lang's hypothesis does not claim to be based upon any 

 experimental evidence, and it may be of interest to see whether 

 there is any actual evidence bearing upon the natural behavior 

 «>f the gametophyte when exposed to conditions similar to those 

 assumed by this hypothesis. 



There are many Bryophytes which are regularly subjected to 

 complete drying up, and I should like to tall attention to their 

 behavior. Most leaf}- liverworts and mosses which grow upon 

 the trunks of trees, or upon exposed rooks, simply dry up com- 

 pletely, and revive promptly so soon as water is furnished them, 

 behaving thus very much as many algae do. In California, and 

 probably the same is true of other similar semi-arid regions, 

 nearly all of the terrestrial liverworts are perennial, and pass 

 through the long, dry summer unharmed. This is well illus- 

 trated by several common species of middle California, such as 

 Fimbriaria califomica, Targionia hypophylla, Fossombronia 

 longiscta, various species of Riceia, etc. In all of these species 

 the apex of the shoot remains alive, being usually more or less 

 perfectly protec ted by overlapping scales or hairs. As soon as 

 the first autumn rains tall, the plants at once resume growth, 

 and in a surprisingly short time develop their reproductive 

 organs. Indeed it is quite possible that the young organs are 

 sometimes already formed at the time the thallus ceases its 

 growth in the spring. 



In mosses it is not uncommon to find bulbils developed, these 

 being merely arrested vegetative shoots, developed from the 

 protonema, or rhizoids. 



Among various liverworts, there have been found tubers of a 

 somewhat different nature, and it is likely that when the thallose 

 forms of semi-arid regions are further studied, these will be 

 found to be commoner than has been supposed to be the case. 

 In the case of the peculiar genus Geothallus of Southern Cali- 

 fornia, the growing point of the thallus, with the tissue adjacent, 

 becomes transformed into a tuber, with a large amount of 

 reserve food developed in the central tissues. This tuber, 

 which is buried in the earth, remains dormant through the 

 summer, but germinates promptly when supplied with water. 



