4IO PROTOPHYTA 



Siphoneas through intermediate forms. The ProtococcaceEe converge 

 also on the boundary line between the vegetable and animal kingdoms ; 

 and, since it has been demonstrated that the power of forming chloro- 

 phyll and starch is not of itself sufficient to determine an organism to 

 belong to the vegetable kingdom, it is impossible to draw a hard and 

 fast line between the Protococcacese and the Flagellate Infusoria, with 

 which they are connected by such forms as Euglena and the Peridinies. 

 The Protococcoidese are divided into two orders, the boundaries of 

 which are very ill-defined : the EremobicB and the Protococcacea. 



Literature. 



Ehrenberg — Die Infusionsthierchen, 1838. 



Nageli — Neuern Algensysteme, 1847, pp. i23-:32 ; and Gattungen einzelliger Algen, 



1849. 

 Braun — VerjUngung in der Natur, 1851 (Ray Soc. Bot. and Phys. Memoirs, 1853) ; 



and Algarum unicellularum genera, 1855. 



(Also the Memoirs referred to under the separate genera, and the literature ot 

 AlgtE generally. ) 



Order i. — Eremobi^ (including Sciadiace^). 



In this ill-defined family, known by some writers as Characiaceae, 

 the limits of which are very difficult to assign, are included a number of 

 genera distinguished from the Protococcaceae by their greater complexity 

 of structure. They are mostly fresh-water, but comprise also a few 

 marine organisms, free-swimming or attached to algae. In the larger 

 number of genera each individual consists of a number of green proto- 

 plasmic bodies, pseudocysts or gonids — that is, masses of chlorophyllous 

 protoplasm of defined outline but not clothed with a definite cell-wall of 

 cellulose — sometimes of considerable size, enclosed in a common trans- 

 parent hyaline envelope, which may be simple or may branch in an 

 arborescent manner. In some genera the hyaline envelope is wanting. 

 Multiplication takes place by simple division, or by the transformation of 

 the gonids into zoospores, which sometimes display a differentiation into 

 larger megazoospores and smaller microzoospores or zoogametes. Although 

 conjugation of these gametes has hitherto been observed only in a few 

 cases, this appears to be the earliest indication among chlorophyllous 

 organisms of a differentiation of sexual elements ; and the Eremobise 

 clearly approach those algae which multiply by conjugation through 

 Botrydium, or through such forms as Endosphasra, Chlorochytrium, and 

 Phyllobium, or again through Hydrodictyon. Lagerheim (Ber. Deutsch. 

 Bot. Ges., 1884, p. 302) asserts the presence of chromatophores in 

 Glaucocystis (Itz.). 



