was found in relation to the total number of deci- 

 meters whose composition was recorded. All tran- 

 sects were located with the intention of providing 

 a typical cross-section of the riffle and were ori- 

 ented at approximately right angles to the direc- 

 tion of water movement (Blum, 195 7) . 



This method also has many drawbacks . It is 

 not applicable to pools and is workable only with 

 difficulty on riffles when the water is 20 cm. or 

 more in depth and turbidity is high — conditions 

 which are likely to be synchronous in a small 

 stream . 



Douglas (1958) has devised several useful 

 instruments for working with epilithic algae . One 

 of these consists of a short, tuft-like brush of 

 nylon bristles, provided with a handle of steel rod. 

 After removing a specimen rock from the water, a 

 50 ml. polythene bottle with bottom sawn off is in- 

 verted over the surface to be sampled . The brush 

 is inserted into the bottle and the rock surface de- 

 limited by the neck of the bottle is scrubbed clean. 

 Washing and brushing are carried out over an en- 

 amel sorting tray so that none of the sample is 

 lost. From the area of the polythene bottle neck 

 and the number of stones used in sampling, it is 

 possible to calculate the total area of stone sur- 

 face thus cleaned. 



Another, more complex tool was devised for 

 the sampling of algae from stones under water. 

 Here the brush used is similar but has a hollow, 

 tubular handle. The upper end of this handle con- 

 nects by means of a length of rubber tubing to a 

 specimen tube. The area brushed is delimited by 

 a steel casing which shields the sampling area 

 from the current and prevents the algae from wash- 

 ing away. A sponge rubber ring at the base of the 

 casing tube provides a tight seal against the rock 

 surface. During sampling with this equipment, 

 algal material brushed from the rock surface is 

 sucked up into the specimen tube through the hole 

 in the brush. From the area covered by the inner- 

 most part of the casing and the number of such 

 areas cleaned, the total area sampled can be cal- 

 culated . 



A third device, employed for the sampling of 

 epiphytes on aquatic bryophytes, was developed by 

 Douglas. This consists essentially of a hardened 

 steel tube or borer sharpened at one end and a wire 

 plunger which can be pushed through it. The borer 

 is forced through the moss layer against the under- 

 lying rock, thus cutting out a small cylinder of 

 vegetation which is subsequently removed by the 

 plunger. An elaborate cleaning process follows. 

 As in the other two methods, counts of the sample 

 are made microscopically after delivering portions 

 of the sample to a counting cell (Douglas, 1958) . 



Among the algae, which the stream collector 

 records by these, or other methods, are forms 

 which are characteristic of standing waters, as 

 well as others which are indifferent; still others 



which are practically limited to running water. 

 Some of these latter forms have been recorded from 

 so many streams, particularly of Europe, that it 

 becomes possible to correlate the data from many 

 surveys and to a degree, to characterize the usual 

 habitat of each alga . Much of the following infor- 

 mation on algal species has been taken from the 

 recent paper of Hornung on the Echaz (1959). 



ECOLOGICAL CHARACTERIZATION 

 OF RHEOPHILIC ALGAE 



Achanthes lanceolata Breb . This is a diatom 

 common and widespread in alkaline streams, and 

 particularly common in springs and small brooks. 

 It exhibits a degree of resistance to certain poi- 

 sons and to sewage pollution (Schroeder, 1939). 

 It exhibits a spring growth maximum, according to 

 Hornung (1959), and a maximum in spring and fall 

 in the results reported by Schroeder. Schroeder 

 states further that in polluted water, its growth 

 maximum is attained in winter. 



Cocconeis placentula Ehr . , frequently an 

 epiphyte, grows best and is most common in run- 

 ning water, in mildly alkaline streams. It is 

 somewhat sensitive to pollutants and seems to ex- 

 hibit a growth maximum in autumn . 



Diatoma vulqare Bory is common and wide- 

 spread, especially in running water, and prefers 

 somewhat alkaline water. According to Kolkwitz 

 (1950) and Hustedt (1944), it is characteristic of 

 the ^-mesosaprobic zone or the region of advanced 

 oxidation of pollutants in a polluted stream. But, 

 I have found its best growth in the oligosaprobic 

 portion of a polluted stream, and various authors 

 have credited it to every one of the principal zones 

 of the saprobic system. In the streams of southern 

 Michigan, which I studied, it was the dominant 

 form, covering all available rocks in the current 

 during the fall months, and again, in spring, 

 (Blum, 195 7). A related species, D_. hiemale 

 (Lyngb.) Heiberg is characteristic of mountain 

 brooks . 



Gomphonema angustatum (Kutz.) Rabh . is 

 typical of small brooks and is adapted to alkaline 

 waters. Kolkwitz (1950) considers it to be an oli- 

 gosaprobic form, but Hornung reports it from highly 

 polluted localities . 



The similar Gomphonema olivaceum (Lyngb.) 

 Kutz. is not confined to running water but forms 

 thick, gelatinous mats in favorable stream situa- 

 tions. In the Michigan streams investigated, it 

 replaced Diatoma yulgare in winter and became a 

 strong competitor for favorable sites with Diatoma 

 in the following spring. In European streams this 

 form seems to be associated with polluted waters, 

 occupying the mesosaprobic zone, according to 

 Kolkwitz (1950), Fjerdingstad (1950), and Liebmann 

 (1951). Melosira varians C.A.Ag. is found in both 



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