36 COLLECTING DIATOMS. 



" The sand in sheltered places, you will observe, is brown in the 

 hollows of the ripple-marks. This is caused by millions of diatomaceous 

 frustules, and we must by all means take home a good store of the 

 brown sand, which by washing easily yields up its riches. 



" Having spent so much time on the marine and brackish-water 

 gatherings, let us turn inland and proceed where the tide ceases to 

 have any influence. To make sure of this, we will take the rails and 

 go to the rocky hills some ten miles distant. Having arrived there, let 

 us examine, in the first place, this rocky streamlet, for I see traces of 

 a brownish covering on the stones, and also some pretty long streamers. 

 Lift the filaments out gently, or you will get little into the bottle. 

 On examination at home you will probably detect Odontidium mesodon, 

 Himantidium undulatum and Anus, with Tabellaria fenestrata and flocculosa. 



" Proceeding a little further, we come to a little water-fall trickling 

 down the surface of the rock and gradually finding its way to the stream. 

 The brown, velvety covering on the stones looks very promising for our 

 purpose, and, if I mistake not, we shall be well rewarded for our 

 trouble in carefully collecting a bottleful of the material, for we have 

 a good gathering of the beautiful Gomphonema geminatum and ventrico- 

 sum mixed with the minute Acnanthidium linearc. The brown mass 

 completely covering the stones in the bed of the stream is Coaonema 

 lanceolatum, not often found so pure. 



"Let us see what causes the green colour on the surface of the mud 

 in the roadside puddle. Ah, this is indeed a treasure ! for it is 

 seldom that Navicula cuspidata occurs as perfectly free from mixtures. 

 The green colour is also remarkable, being so different from the usual 

 brown endochrome of most diatoms. 



"Here is another roadside puddle left by the recent rain; and see 

 what a brown coating has grown at the bottom in so short a time. At 

 any rate, we have here Diawmacece in abundance, though small in size, 

 probably Nitzschia palea and Pinnularia pygmcea. 



"Proceeding further inland, we are supposed to be passing a water- 

 mill ; and, as the mill-race is covered with confervoid growths, let us 

 examine some of the coating from the wooden aqueduct. The brown 

 streamers are in all probability Diatoma vulgare and elongatum, and the 

 beautiful stellate form is the local Asterionclla formosa, which, by the 

 way, seems to select its habitat always in some out-of-the-way place> 

 such as the present one in the mill aqueduct, water tanks and reservoirs. 



" Having climbed up some distance on the hillsides, let us collect 

 some of the weeds from the sides of the boggy pool, for in such 



