604 MICROSCOPIC FORMS OF VEGETABLE LIFE THALLOPHYTES 



is that of Eunotiece, of which we have already seen a characteristic 

 example in Epiihemia turgida (fig. 446). The essential characters 

 of this family consist in the more or less lunate form of the frustules 

 in the lateral view (fig. 446, B), and in the strife being continuous 

 across the valves without any interruption by a longitudinal line. 

 In the genus Eimotia the frustules are free ; in Epithemia they are 

 very commonly adherent by the flat or concave surface of the con- 

 necting zone ; and in Hlmantidium they are usually united into 

 ribbon-like filaments. In the family JSt&ridiece we find a similar 

 union of the transversely striated individual frustules ; but these are 

 narrower at one end than at the other, so as to have a cuneate or 

 wedge-like form, and are regularly disposed with their corresponding- 

 extremities always pointing in the same direction, so that the fila- 

 ment is curved instead of 

 straight, as in the beauti- 

 ful Meridian circtdare (fig. 

 448). Although this plant, 

 when gathered and placed 

 under the microscope, pre- 

 sents the appeai-a nee of 

 circles overlying one an- 

 other, it really grows in a 

 helicoid (screw like) form, 

 making several continuous 

 turns. This diatom abounds 

 in many localities in this 

 country ; but there is none 

 in which it presents itself 

 in such rich luxuriance as 

 in the mountain-brooks 

 about West Point in the 

 United States, the bottoms 

 of which, according to Pro- 

 fessor Bailey, ' are literally 

 covered in the first warm 

 lays of spring with a fer- 

 ruginous-coloured mucous 

 matter, about a quarter of 



an inch thick, which, on examination by the microscope, proves to 

 be filled with millions and millions of these exquisitely beautiful 

 siliceous bodies. Every submerged stone, twig, and spear of grass is 

 enveloped by them, and the waving plume-like appearance of a fila- 

 mentous body covered in this way Is often very elegant,' The frus- 

 tules of Meridian are attached when young to a gelatinous cushion ; 

 but this disappears with the advance of age. In the family Licmo- 

 frfiorvce iilso the frustules are \\ edge-shaped ; in some genera they have 

 transverse markings, whilst in others these are deficient; but in 

 most instances there are to be observed two longitudinal suture-like 

 lines on each valve (which have received the special designation of 

 vittce) connecting their two extremities. The newly formed part of 

 the stipe in the genus A/V/m/////,//-^, instead of itself becoming double 



FIG. 450. Licmojiliuni JI<iln'lUit . 



