236 Evans: ArR CHAMBERS OF GRIMALDIA FRAGRANS 
Ricciocarpus, Peltolepis, Sauteria, Clevea, Plagiochasma, Reboulia, 
Grimaldia, Neesiella, Cryptomitrium, Asterella and Bucegia; while 
the Marchantia type occurs in Corsinia, Targionia, Conocephalum, 
Lunularia, Preissia and Marchantia. The reduced air chambers 
of Cyathodium conform best perhaps to the Marchantia type, in 
spite of the absence of green filaments, while the adult thallus of 
Dumortiera lacks air chambers altogether. 
The genus Grimaldia Raddi, as understood by most recent 
writers, contains about half a dozen species. The most widely 
distributed of these is G. fragrans (Balb.) Corda, which is found in 
Europe, Asia and North America. Other well-known species, 
closely related to G. fragrans, are the Mediterranean G. dichotoma 
Raddi and the Californian G. californica Gottsche. In the eastern 
parts of the United States G. fragrans is sometimes locally abun- 
dant, preferring sunny trap ridges and growing on earth among 
rocks, rather than on the rocks themselves. It was in such a 
locality as this, on West Rock Ridge, near New Haven, Connecti- 
cut, that the material used in the present study was collected. 
The narrow thallus is firm and compact and produces an abun- 
dance of purple ventral scales with bleached-out appendages. 
The upper surface is grayish green and shows no indications of the 
boundaries of the air chambers beneath the epidermis. The 
margins, as well as the ventral surface, are more or less pigmented 
with purple. The species is markedly xerophytic, the margins 
becoming involute when dry, thus covering over and protecting 
the upper surface. 
THE AIR CHAMBERS OF THE MATURE THALLUS 
The green tissue of the thallus in Grimaldia has been repeatedly 
described, most of the observations having been based on either 
G. fragrans or G. dichotoma. Unfortunately the descriptions show 
marked discrepancies. Stephani (11), for example, states that 
the air chambers are densely filled with erect green filaments 
composed of long cylindrical cells, and K. Miiller (6, p. 259) 
notes the presence of vertical plates of cells in addition to the 
filaments. Schiffner (9, p. 309) criticizes these descriptions. 
According to his account the chambers of Grimaldia undergo a 
secondary partitioning by means of irregular green lamellae which 
