33- Cdvers : Ahfes on Yorkshire Bryophytes. 



ot the apical i;Towing--point, entirely bears out Leitgeb's view""' 

 that the lamellae alone represent the leaves, and that the wing- 

 which carries them is simply a lateral expansion of the stem. 



The excellent general account given by Leitgeb in his 

 * Untersuchungen ' is based chiefly on his investigation of P. 

 Preissii, though he also examined a few plants of P. Ralfsii. 

 Leitgeb found that in P. Preissii the apical cell was of the 

 wedge-shaped or ' two-sided ' type, only two lateral series of 

 segments being cut off, as in Fossombrouia, whereas in P. Ralfsii 

 the apical cell is tetrahedral, as in the majority of the leafy 

 Jungermanniales. He states that in other respects the two 

 species closely agree, but in the specimens of P. Ralfsii 

 examined by me the posterior portion of the shoot is quite 

 cylindrical and shows no trace of the marked dorsal groove 

 described and figured by Leitgeb in P. Preissii. 



An interesting feature in the biology of Peialophylliiin is the 

 formation of tubers containing reserve food-materials. Leitg'eb 

 describes and figures plants of P. Preissii in which the anterior 

 end of the shoot is prolonged into a cylindrical tuberous out- 

 growth, though he gives no details as to the contents of these 

 protuberances. In P. Ralfsii I have not observed any out- 

 growths of this kind, but have found tubers of another type, 

 closely similar to those described and figured by Campbellf in 

 Geothalliis tuberosus, an interesting Californian species which 

 also shows a striking resemblance to Petalopliylliiui in general 

 structure and in habitat. Lindberg states that during the 

 summer months the plants of P. Ralfsii become partially or 

 completely buried in the sand, but Mr. Ingham, who has visited 

 the habitat of this species on Coatham Marshes at frequent 

 intervals throughout the summer, informs me that, so far as his 

 experience goes, the sandy soil in which the plant grows, in 

 company with Pallavicinia Flotovoiana, does not at any time of 

 the year become dried up but is invariably moist and spongy, 

 and that the plants do not become buried in the sand but are 

 sheltered by short grass and other vegetation. The tubers 

 referred to are found in plants collected in summer ; on section- 

 ing a plant taken in May or June, the tissue of the stem, 

 immediately behind the growing-point, is found to have become 

 thick and fleshy, forming an ovoid tuber which projects from 

 the ventral surface and bears numerous rhizoids. In sections 



* Untersuchungen iiber die Lebermoose, Heft 3, p. 127. 

 t ' The Development of Geothalliis tuberosus,' Annals of Botany, \'ol. 10, 

 1896, p. 489. 



