Marine Groves and Gardens 127 



The sea lettuce is the common food of many creatures 

 of the sea. Indeed the human species itself has not 

 disdained to make it serve its needs. Under the name 

 of "oyster green" this seaweed was once prepared for 

 the table as a wholesome delicacy. But its value to the 

 animals of the sea is twofold; besides serving as a 

 source for food it gives off considerable oxygen in the 

 water so that they may breathe. While all seaweeds 

 give off more or less oxygen this property of Ulva is 

 noteworthy and for that reason it makes a most desir- 

 able plant for aerating the indoor aquarium. It adapts 

 itself readily to confinement and will thrive in situations 

 that are fatal to other marine plants. 



Next to Ulva, perhaps the most familiar seaweed is 

 Fiiciis. Fucus, or the rockweed, is far different from 

 Ulva, however, in color, form, and habitat. It is one 

 of the brown seaweeds, although its color is more often 

 an olive green, and grows in its greatest profusion 

 between the tide marks on exposed rocky shores. The 

 tough and leathery texture of this plant denotes its 

 character. Holding fast with its suckerlike disk to the 

 rocks of rugged shores, it breasts with impunity the 

 shattering force of the driving surf. But its hardiness is 

 exemplified not merely in the ability to live in a pound- 

 ing sea; it thrives throughout the winter, and, under 

 the scorching rays of the summer sun, during the fall 

 of the daily tides, it survives temperatures that would 

 shrivel the sea lettuce into a formless cinder. 



In further contrast to the simplicity of green sea- 

 weed is its higher organization, or differentiation of 

 parts. Some members of this genus have a distinct 

 midrib. All the plants are forked and flat; that is, 



