6 HUMPHREY 
Fossombronia 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 18, 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 vigorously, 
a considerable number of plants of Hossombronza longiseta, 
Anthoceros pearsont, Targionia hypophylia, 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 anything 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 Hossombronza 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 phymatodes is a matter that has not yet 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 commonly supposed but is pri- 
marily due to the formative influence of light. 
As elsewhere stated, some plants of Hossombronza longiseta 
were studied in which the rhizoids were apparently free from 
1 Peirce, 1906: Studies of Irritability in Plants. Annals of Botany, Vol. XX, 
No. LXXX, p. 459. 
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