Trentepohliacece 93 



may conjugate in pairs and produce resting hypnospores. In the 

 conjugation of the zoogonidia the ends which do not bear the cilia 

 first fuse together. 



L. Mediciana Borzi is a rare plant found amongst Sphagnum and Utri- 

 cularia in bogs and boggy pools. It is only known from Yorkshire and 

 Sicily. Diameter of cells up to 20 /x. 



Family 7. TRENTEPOHLIACEJE. 



This family is only represented in the British Islands by a 

 few species of the genus Trentepohlia. The thallus is aerial, 

 filamentous and branched, generally occurring on rocks or on the 

 bark of trees. The filaments may be very short and more or less 

 creeping, or they may form erect tufts or closely matted cushions. 

 The cells are sometimes cylindrical and sometimes moniliform or 

 torulose, and the branches usually show a slight attenuation. The 

 cell-walls are firm and frequently exhibit external sculptures. 

 Brand 1 states that the longitudinal walls are lamellose, but the 

 transverse walls are simple ; and that the cellulose caps which are 

 so frequently developed at the extremity of a branch, are the 

 remains of dead, terminal zoogonidangia. This is certainly 

 not true of some species, however. Each cell contains one 

 nucleus and usually a number of disc-like, parietal chloroplasts 

 without pyrenoids. The colour of these plants is usually some 

 shade of brown, brownish-red, or orange-red, the chlorophyll being 

 masked by the presence of a pigment known as hsematochromin, 

 which is frequently dissolved in a quantity of oil. 



In the Trentepohliacese the zoogonidia are only produced in 

 specially differentiated cells or zoogonidangia. This character, the 

 absence of terminal hairs and the nature of the chloroplasts, are 

 the principal distinctions between the Trentepohliaceas and the 

 Chastophoracese. The zoogonidangia are developed singly or in 

 clusters, either terminating a branch and so arresting its develop- 

 ment 2 , or developed laterally on the branches, or more rarely in 

 the axil of a branch. They are sessile or stalked, generally 

 ellipsoid or ovoid in shape, and they open by means of a terminal 

 or subterminal pore. The zoogonidia, which are of two sizes, are 

 pear-shaped and furnished with two cilia. The smaller micro- 

 zoogonidia have been observed to conjugate in pairs, but all are 



1 F. Brand in Beihefte z. Bot. Centralbl. xii, 1902. 



2 The development is only arrested temporarily as the terminal cell or supporting 

 cell often grows through the empty zoogonidangium. 



