76 GENEEAL HISTOEY OF THE OFUSOEIA, 



at the bottom of pools, or on the surface of mud ; the freshwater species 

 often by the road-side ; the marine forms usually near high-water mark. Am- 

 pMpleura injiexa and A. scalaris congregate, in large brown stains or spots, 

 on the muddy sides of rocks, whilst other species, for instance CampijlodiscuSj 

 and Coscinodiscus concinnus, form similar collections, but prefer more shady 

 situations. 



'' The sides of ditches in brackish marshes are very prolific, especially after 

 spring-tides, and in situations not again covered until the next high-tides. 

 We may expect to gather in such places species of Smnrella, Navicida, Pleu- 

 7'osigma, Ceratoneis, Amphiprora, Amphora, &c. The soil about the roots of 

 rushes and of other plants inhabiting salt marshes often aiford interesting 

 forms, but seldom in abundance. We find there species of Coscinodiscus and 

 of Zygoceros ; but such are obtained more abundantly from the mud or from 

 the washings of bivalve shells brought uj) from deep w^ater or collected at the 

 mouths of rivers. Oyster-beds are in general productive. The Bac'illaria 

 paradoxa inhabits ditches in w^hich the water is nearly fresh, and is frequently 

 obtainable from the scum diiven from the siuface to the banks. 



" Pew Diatomeae are peculiarly autumnal ; we have, however, gathered 

 Homoeocladia Martiana, Berheleya fragilis, DicTcieia pinnata, and Striatella 

 umpmictata, chiefly at that season. . 



" On warm siunmer days, Diatomeae, with various microscopic Algae and 

 Fungi, rise to the siu-face of water by the disengaged oxygen gas still ad- 

 hering to them and buojing them up, and there form a dehcate film or a 

 scum, and at times even a layer of considerable thickness. Such collections 

 are rich in species of Navicida, CgmheUa, Surirella, and Si/nedra. When an 

 entangled larger mass is formed, there is usually one prevailing species. 

 Specimens of Fragilaria are generally found on decapng wood or leaves, 

 or amongst Confervae diffused in the water. From the drainings of Sphagnum 

 may often be obtained Synedra biceps and various species of Himantidium. 

 Boggy soil, especially when situated on a slope, affords various species of Epi- 

 themia and Navicula ; so hkemse does the soft matter on rocks on which water 

 constantly trickles. Washings from oysters and the refuse raised by trawlers 

 are usually rich in spheres of Coscinodiscus, Actinoptychiis, Pleurosigma, Di- 

 pJoneis, Navicida, Dictyocha, &c. The same kind of washings from sheltered 

 harbours give Surirella fastuosa, Auliscus scidptus, together with species of 

 Campylodiscus, Triceratimn, &c. Washings of corallines are like^vise some- 

 times productive." 



Mr. Norman supplies us with the following hints : — " The most interesting 

 forms occur in salt water, especially in shallow lagoons, saltwater marshes, 

 estuaries of rivers, pools left by the tide, &c. Their presence in any abun- 

 dance is shown by the colour they impart to the aquatic plants they are 

 attached to ; or when found on mud, by the yellowish-brown film they form 

 on the surface, and which, if removed with a spoon mthout disturbing the 

 mud, will be found a very pure deposit. 



" Such collections are best put at once in bottles, or even partially dried 

 and wrapped in pieces of paper or tin-foil. When placed in bottles, a few 

 drops of spirit are advantageously added. In all cases it is essential that the 

 locahty whence obtained should be plainly written on each package. Capital 

 gatherings are obtainable by carefully scraping the brownish -coloured layer 

 from mooring-posts, or the piles of wharfs or jetties. 



"" In clear running ditches, the plants and stones have often long streamers 

 of yellowish-brown slimy matters adhering to them, generally composed almost 

 wholly of filamentaiy species. The layers of Diatomaceous fronds on the 

 surface of mud are often covered with bead-hke bubbles of oxygen, which 



