PHYSIOLOGY AND MORPHOLOGY OF CALIFORNIA HEPATIC: 35 
notably an Italian form in which he observed entire portions of 
the thallus developed into tuber-like structures. Stephani’ has 
also described similar structures for /tzccza bulbtfera. None of 
our Californian Riccias has yet been described as bearing 
tubers or tuber-like growths, though /t¢ccca trichocarpa, men- 
tioned elsewhere in this paper, is well adapted to withstand 
severe exposure, the thallus being densely clothed with tawny 
sete .3 to .65 mm. long, with those toward the apex in as many 
as eight to twelve series, affording a very effective protection 
against excessive drying. ‘Though these tuber-like structures 
wherever they have been examined are always found to con- 
tain large quantities of reserve food, there is little doubt that 
they are instrumental as water-storage organs. 
STUDIES IN THE GERMINATION OF SPORES. 
In a previous paper the writer has described and figured the 
germination of the spores of Mossombronza longiseta. ‘The 
results of experiments then carried out showed the early devel- 
opment of this species to agree closely with certain forms, not- 
ably Spherocarpus californicus, investigated by Campbell.’ 
Most of the hepaticee of this region produce spores character- 
ized by a heavy, more or less sculptured exosporium which 
Leitgeb * found to consist of two parts or layers of which the 
inner belongs to the spore itself and is the exine, while the 
perinium or outer layer is formed later and consists of parts of 
the sporocyte. Leitgeb suggests the probability of the perinium 
as a protection against drought but in the light of more recent 
studies of certain forms producing thick-walled spores, e. ¢., 
Corsinia, Pretssia, Anthoceros and Spherocar pus, it may be held 
that the perinium can certainly have nothimg to do with a rest- 
ing period, for spores of these forms germinate readily within a 
few days after being sown. As to the thick exosporium fur- 
nishing a protection against excessive dryness there can be little 
doubt, although such forms as Corsznza and the aquatic Ric- 
1 Stephani, 1898: Species Hepaticarum. Bull. de l’Herb. Boiss., Vol. VI, p. 
333 
2 Campbell, 1896: Notes on Spherocarpus. Erythea, Vol. IV, No. 5, Pl. 2. 
* Leitgeb, 1884, Ueber Bau und Entwicklung der Sporenhaute, Graz. 
