CORAL ALGAE 



205 



pores at the surface (Fig. 104), in Lithophyllum by only one 

 (Fig. io5).i 



Another difference between Lithothamnion and Litho- 

 phylkim has been described. In the former there is a marked 

 distinction between the outer layers of small cubical cells 

 constituting the Perithallium and the inner layers of larger 

 and longer cells constituting the Hypothallium. In Litho- 

 phyllum the hypothallium is represented by a single layer 

 of cells or is entirely wanting. 



Enough has been said, perhaps, to indicate to the reader 

 that there is a scientific distinction of some importance 

 between these two genera, and that the accurate determina- 



FiG. 104. — Section of a tetra- 

 sporangial conceptacle of a Litho- 

 thamnion showing two tctrasporcs 

 (t, t), and the surface perforated b}' 

 several pores. 



Fig. 105. — Section of a young 

 tetrasporangial conceptacle of a Litho- 

 phyllum showing two tctraspores (t, t), 

 the surface perforated by one pore and 

 a tuft of paraphyses {p) at the base. 



Figs. 104 and 105 from Engler and Prantl. 



tion of the character that separates them requires some 

 special skill and scientific appliances. 



It has been noted (p.. 203) that many of the species of the 

 old genus Lithophyllum have been separated by Foslie 

 into a new genus Goniolithon. The difference between 

 these two genera lies in the character of the asexual con- 

 ceptacle. In Goniolithon the tetrasporangia are evenly 

 distributed over the floor of the conceptacles, whereas in 

 Lithophyllum they are formed only on its sides, the centre 

 of the conceptacles being provided with papilliform pro- 

 cesses called the Paraphyses (Fig. 105). 



1 For further information on this point see A. Engler and K. Prantl, 

 Die natiirlichen Pflan:enfamilien, Nachtrag, igii ; NicoUs, University of 

 California Publications : Botany, vol. iii., 1908 ; and Mme. Paul Lemoine, 

 C. R. Paris, Feb. 15, 1909. 



