FIXED PLANTS 73 



we may premise our remarks by the statements 

 (1) that any exhaustive collection of any group from 

 any locality is of great value, and (2) that only 

 groups which suit the environment (particularly the 

 nature of the bottom, whether sand, mud, rock, or 

 weed) can be collected exhaustively enough in a few 

 months. 



In selecting the groups to be collected, we have to 

 consider the life-histories of the animals or plants 

 which form these groups, particularly the point whether 

 they do or do not possess larvae which are capable of 

 living as larvae for long periods of time in the surface 

 waters of the sea, and are therefore capable of being 

 transported by ocean currents from their original 

 homes, often for many thousands of miles. Such 

 larval forms are not numerous among the seaweeds, 

 though other means of dispersal by floating pumice and 

 timber are peculiarly adapted to them. The same 

 genera of plants are found over wide areas, but we give 

 plants first place, since they form the most important 

 source of food for animals, and may kill out or prevent 

 the growth of other sedentary organisms. They may 

 inhabit any area, some (such as Cymodocea and 

 Halophila, dicotyledonous forms) loving shallow flats 

 over which the sea rushes ; the former are quite grass- 

 like in appearance. The home of plants, however, is 

 essentially on rocks over which they form, perchance, 

 a calcareous crust (Squamariaciae), rounded or branched 

 living growths (Lithothamnia), interlaced " mosses," and 

 low " herbs." Algae, such as those on our temperate 

 shores, are scarce ; but there is a great variety of these 

 other forms. The methods of selecting and observing 

 marine plants are discussed in Chapter IV. (p. 152), 

 and we would only further emphasize the importance 

 of securing large series of specimens, particularly of 



