38 COLLECTING DIATOMS. 



at present examining is several feet thick, and has at some remote 

 period formed the bed of a lake, the diatoms accumulating at the 

 bottom until the present thickness was attained. You will observe that 

 the endochrome has been removed by long rotting, and the entire 

 mass is now composed of the pure white siliceous valves. Pray also 

 observe that this richness in silex suits the cereal crops growing over 

 it, but does not seem to furnish much nutriment to the potatoes and 

 turnips. 



" The adjacent peat-beds may also be examined, for frequently rare 

 Diatomacea^ are found in the turf which is cut for fuel. 



"The dark, hairlike mass growing on the wood-work of this sluice- 

 gate is a nice pure gathering of Schizonema neglectum, the frustules 

 arranged in regular rows in the interior of the long filaments. 



" Before leaving this pond, let us pull out a mass of the Myrio- 

 phyllum, which seems rusty in color. Well ! here is a medley of forms, 

 but the gathering is worth bottling up, owing to the abundance of 

 Amphipleura pellucida. 



" The clear ditch by the roadside is a likely place for such forms 

 as Pleurosigma attenuation, Spencerii, and lacustre, Nitzschia linearis and 

 tenuis, Surirella ovata, Navicula elliplica and Cymbeila maculata. 



" The yellow mass attached to plants a little further on is Cydotella 

 operculata, Amphora ovalis, and Nitzschia sigmoidea, while the brown 

 covering on the Anacharis is GompJionema tenellum, dichotomum, and 

 curvaium. The stones in the running beck, issuing from the clear spring 

 close by, are covered with long, yellowish-brown streamers, which are 

 well worth collecting. Take them out very gently, for they are very 

 fragile, and likely to drop again into the water. The species is the 

 beautiful Meridion circulare, with Melosira varians. 



At the bubbling spring itself, which forms the head of the streamlet, 

 the sand, which is tossed and heaved about by the ascending water, 

 seems tinted of a brown color. Let us secure some of the sand, when 

 we shall find the brown color is caused by a dense parasitic growth 

 of Odoniidium Harrisonii quite pure. 



" Farther on the dark brown streamers must be collected, for here 

 are two species of Fragilaria, capueina and virescens mixed with Dia- 

 toma elongatum. The stones and aquatic plants are likewise covered 

 with a dense brown coating of Synedra radians and ulna, species found 

 in almost every clear water ditch. 



" The boggy place where the plants are coated with a yellow coat- 

 ing of the oxide of iron, is not to be passed without collecting a little 



