26 ERYTHEA. 



dredge, and in the other allowing it to slide over without catching. 

 The stony or shelly bottoms of tideways and off points where the 

 currents set strongly are usually clothed thickly with algse from the 

 elitoral zone up to high-water mark. These are excellent places to 

 dredge. Long stretches of mud or sand yield few if any species of 

 the literal or upper sublitoral zones, but may be places where many 

 of the species of the deeper or even the shallower waters are drifted 

 in and may be taken by wading or with the boat. A hand-net is 

 very useful to catch floating specimens, especially if there is any 

 decided curreut. Pebbly shores are often good, and especially when 

 the pebbles are of large size and more or less firmly fixed in position. 

 But the rocky shores are the ones to which the collector is attracted 

 most strongly. The surface of the rock affords an excellent foothold 

 for almost all kinds of algse, from the tightly clinging crustaceous 

 species to the long, erect, and almost shrubby kelps. Again, upon a 

 rocky shore, the irregularities of the surface are usually so pronounced 

 that wlien the tide is out, large pools of water are left between tide- 

 marks, in which many and rare forms grow within easy reach of the 

 collector. A shoi*e well supplied with tide-pools is the most desirable 

 of all. The nature of the literal region of the shore is so accurately 

 and plainly indicated as regai'ds the several features just mentioned, 

 on the charts of the Coast and Geodetic Survey, that good collecting 

 places may be selected almost without a visit. Something may also 

 be told of the nature of the sublitoral and elitoral zones from the 

 charts where the chax-acter of the bottom is indicated. 



The pools and ditches of the salt marshes are generally the homes 

 of characteristic species, and may be visited at almost any condition 

 of tide, although, in general, the forms display themselves most 

 plainly when the tide is in and the pools and ditches are full of 

 water. The floating scums of such ditches and pools, the films 

 covering the surface of the damp earth between the marsh-grasses, 

 and even coating, in many cases, the stems of the various flowering 

 plants inhabiting the marshes, are of especial interest. Even mud 

 from the bottoms of the pools and ditches, brought home and allowed 

 to stand in dishes, will often become covered with films of different 

 blue-green algse which do not otherwise give evidence of their 



presence. 



Collecting Apparatus. — An experienced collector takes but 



