280 ALGsE 



smaller swarm-spores has been observed in Chroolepus (Ag.), but they can 

 also germinate without conjugation. Chroolepus also produces resting- 

 spores. Of this genus one species, C. aureum (Ktz.), is common on walls 

 and rocks, and another, C. umbrinum (Ktz.), occurs on the bark of trees. 

 C. lolithus (Ag.) is one of the few algae that grow in perfectly dry situations 

 on gneiss &c., and on a siliceous rock in the Hartz Mountains known as 

 ' violet-stone.' The genus Trentepohlia (Mart.) is now merged by many 

 writers in Chroolepus. Wille has pointed out that the organism de- 

 scribed as Gongrosira de Baryana (Rbh.), which grows attached to the shell 

 of fresh-water molluscs as a green velvety coating, is a form of Chroolepus 

 or Trentepohlia. 



The genera included under the Chroolepidese by Borzi in addition to 

 Chroolepus and Trentepohlia are Microthamnion (Nag.), Acroblaste 

 (Reinsch), Leptosira (Borz.), Chlorotylium (Ktz.), and Pilinia (Ktz.). 

 Acroblaste grows in salt water attached to mussel-shells, but its position 

 here is doubtful. Leptosira produces zoospores, some of which germi- 

 nate directly, while others are said to conjugate, but in a manner different 

 from other zoogametes, by the end which does not bear the cilia. To 

 this family probably belongs also Trichophilus (Weber), a remarkable 

 alga parasitic on the hairs of a sloth, which produces two kinds of 

 zoospore (Bot. Centralblatt, vol. xxxiv., 1888, p. 161). 



LITERATURE. 



Caspary Flora, 1858, p. 579. 

 Hildebrand Bot. Zeit., 1861, p. 81. 

 Gobi Bull. Acad. Sc. St. Petersbourg, 1872. 



Schnetzler Bull. Soc. Vaud. Sc. Nat., 1879, p. 267 ; 1880, p. 13 ; and 1883, p. 53. 

 Borzl Studi Algologici, 1883. 



Wille Pringsheim's Jahrb. wiss. Bot., 1887, pp. 426 and 484. 

 Wildeman C. R. Soc. Roy. Bot. Belgique, 1888, p. 140. 

 De Toni Notarisia, 1888, p. 581. 



Class XVI. Multinucleatae. 



In this newly-constituted group are included the four orders of 

 Siphoneae, Botrydiaceae, Dasycladaecea, and Siphonocladaceae, the near 

 relationship of which to one another is scarcely doubtful, although the 

 first displays sexual reproduction of a high type, with strongly differ- 

 entiated antherids and oogones, which are not found in the other 

 orders. All the orders nre also propagated non-sexually by zoospores. 

 Their common characteristic is. the extraordinary development in size 



