258 HeteroTiontce 



T. bombycinum (Ag.) Derb. & Sol. ( Conferva bombycina Ag.) is general 

 throughout the British Islands; diam. of cells 8 15 p.; fig. 121 A G. A 

 small form of this species [forma minor (Wille) nob.J is also very common; 

 diam. of cells 5 6'5 p, : fig. 121 H and I. T. affine (Ku'tz.) nob. (^Conferva, 

 affinis. Klitz.) is the thinnest species with the most elongate cells, and the 

 chromatophores are few and irregular; diam. of cells 5 5'4 p.. T. obso- 

 letum nob. ( = Conferva obsoleta West & G. S. West) is a much rarer species ; 

 diam. of cells 19 21 p.. 



Genus Bumilleria Borzi, 1895. The cells of this genus are 

 arranged in long filaments which differ from those of Conferva 

 principally in the structure of the cell-wall. The latter is 

 practically homogeneous and does not readily break into H -pieces. 

 The pectose constituents instead of forming closely apposed layers 

 may form a distinct mucous cylinder in which the cells appear to 

 be embedded. The chromatophores are small, pulvinate and 

 parietal. 



B. pumila West & G. S. West is the only known British species ; length of 

 cells 56 p.; diam. 4'8 5'7 p.; fig. 121 J. 



Family 3. BOTRYDIACE^. 



This family is well marked off from the other groups of the 

 Confervales by the form of the plants alone. Each individual is 

 a rounded coenocyte of macroscopic size and is attached to damp 

 mud by well-developed ' rhizoids.' The chromatophores are very 

 numerous and the methods of reproduction are somewhat 

 diversified. 



Genus Botrydium Wallroth, 1815. The plants consist of 

 green, pear-shaped or spherical coenocytes of considerable size, 

 growing on damp mud into which they are rooted by a branched 

 system of colourless rhizoids. The coenocytes are vesicular, with a 

 lining layer of protoplasm in which are embedded numerous nuclei 

 and chromatophores. The latter are irregular in form, more or less 

 evenly scattered in one or more layers through the lining proto- 

 plasm, and are generally in close contact with the nuclei. Bodies 

 of the nature of pyrenoids have been observed in the younger 

 stages of the plant, but starch is not formed. The rhizoids possess 

 protoplasmic contents and many nuclei. Wager has observed 

 mitotic division of the nuclei and states that the chromatic sub- 

 stance appears to reside wholly in the nucleolus. 



This plant reproduces itself asexually in a great variety of 

 ways, depending largely on the 'conditions of environment, any 



