O HUMPHREY 



J^ossombronia longiseta collected in southern California where 

 the dry season is longer, this tuberous growth is considerably 

 more marked than in the case of plants in the northern half of 

 the state. Owing to the earthquake of April i8, 1906, a break 

 occurred in a water-pipe not far from Stanford University. As 

 a consequence a considerable tract of ground was well irrigated 

 throughout the past, very prolonged dry summer. Upon this 

 thoroughly moistened soil the writer found, growing vigorousl}', 

 a considerable number of plants of Fossombronia longiseia^ 

 Anthoceros -pearsoni, Targionia hypophylla, and some species 

 of the more common mosses. Here were growing a number 

 of plants accustomed to summer desiccation and it occurred to 

 the writer that under these conditions of increased humidity 

 certain structural changes might result both in the development 

 of the gametophyte and sporophyte. 



Careful examination of a large number of these plants re- 

 vealed no evidence of an3'thing in the nature of a tuberous 

 growth in any part of the thallus though all plants examined 

 showed fungus infection. It would seem therefore that this 

 instance would lend some support to the inference that, so far 

 as our species of Fossombronia is concerned, these small tuber- 

 like structures are purely adaptive and their development 

 depends largely upon certain external factors. Whether growth 

 under similar conditions would result in the reduction or dis- 

 appearance of the tubers in such plants as Geothallus tubero- 

 sus or Anthoceros ■phymatodcs is a matter that has not 3'^et been 

 tested. In these forms the tuber is a well-marked and doubtless 

 long-established modification of the thallus and if reduced at 

 all would probably require a considerable period of time during 

 which conditions of constant moisture are allowed to act. 

 Peirce,' '06, has demonstrated that such a well-marked char- 

 acter as the dorsiventrality of certain liverwort gametophytes is 

 not a hereditary character as commonl}^ supposed but is pri- 

 marily due to the formative influence of light. 



As elsewhere stated, some plants of Fossombronia longiseta 

 were studied in which the rhizoids were apparently free from 



' Peirce, 1906 : Studies of Irritability in Plants. Annals of Botany, \o\. XX, 

 No. LXXX, p. 459. 



