300 



Ulotrichales 



radians Peter) is epizootic on the carapace of the European water-tortoise (Cleminys 

 caspica). Ulvella fucicola Rosenv. is partially parasitic 011 plants of Fucus, causing a 

 destruction of the peripheral cells. 



It is probable that all the Ulvellese have originated from the Chsetophorese by a 

 reduction and modification of the branch -system consequent upon the adoption of a 

 completely epiphytic mode of life. 



Arthrochsete should be compared with Pseudochsete since both these genera are really 

 intermediate between the Chsetophoreye and the Ulvelleae. 



Fig. 193. A C, OchloclitEte ferox Huber. A, young plant, x 383 ; B, section through a part of 

 plant with zoogonidangia, x 383 ; C, zoogonidia, x 1050. D and E, Chsetobolus gilbus 

 Eosenv. D, section through plant, x 316 ; E, small part of same, x 526. (A C, after 

 Huber; D and E, after Rosenvinge ; from Wille.) 



Sub-family MICROTHAMNIE.E. This group as here defined is equivalent 

 to the Microthamniacese (West, '04) and almost the same as the Leptosireae 

 (Wille, '09). The Microthamniacese was originally separated from the 

 Chsetophoracese on two characters : first, the absence of murticellular hairs, 

 arid secondly, the restricted origin of the zoogonidia. Recent investigations 

 have shown, however, that neither of these characters is sufficiently 

 pronounced or constant to be utilized as a basis upon which a family 

 ' Microthamniaceae ' can be rightly established. 



The thallus is branched, with or without a mucous investment, sometimes 

 procumbent, but more often branched so as to form a pulvinate mass. The 

 branches are usually attenuated, but never piliferous, and hairs (or seta) are 

 never developed. The cells vary much in external form, and in some species 

 of Endoderma and Gongrosira are most irregular (consult fig. 194 E}. In 



