Bittersweet Nightshade Swamps Monkey Flower Swamps Asters (many species) Woods Bluets Fields Blue Curls Fields Brown or Green Common Cat-tail Swamps Narrow-leaved Cat-tail Swamps Curled Dock Fields Halberd-leaved Orache Marshes Sea Blite Marshes Chapter 4 LIFE AT THE EDGE OF THE SEA Everyone likes to be a beachcomber! And each passing tide exposes the secrets of the sea to those interested enough to take a closer look. Suppose that we examine this world which is revealed to us twice daily. “WEEDS” OF THE SEA The sea holds many strange plants that have taken on fantastic sizes and shapes because of their underwater environment. In spite of their size, these plants are usually among the most primitive—a simple sheet of cells. Such plants are called _algae_ and are subdivided according to their colors. _The Brown Algae_ [Illustration: Common Rockweed] Common Rockweed (_Fucus_, several species) Brown, flattened body Central midrib Stem has air bladders The bladders are filled with air, and children like to squeeze them to hear their pop. These bladders cause the plant to float upright, thus keeping all its sides in contact with water. [Illustration: Nodose Rockweed] Nodose Rockweed (_Ascophyllum nodosum_) Thin, round stem No central midrib When dried by the sun, this plant makes an interesting and lasting souvenir, for it turns a lustrous black. [Illustration: Common Kelp] Common Kelp (_Laminaria agardhii_) Broad, flat blade Several feet in length The kelps of the Pacific grow several hundred feet in length, making them the largest of the algae and among the very largest plants. [Illustration: Fingered Kelp] Fingered Kelp (_Laminaria digitata_) Many blades, extending like fingers on a hand All kelps have a rootlike structure called a “holdfast” to serve as an anchor. Often tiny sea creatures dwell in among the holdfast. Why not take a look? [Illustration: Perforated Kelp] Perforated Kelp (_Agarum cribrosum_) Central midrib Broad blade punctured with hundreds of holes In Asia this kelp is farmed for food called agar. An extract of the plant, agar-agar, is used in the laboratory as a culture medium for bacteria and other disease-producing organisms. _The Green Algae_ [Illustration: Sea Lettuce] Sea Lettuce (_Ulva species_) A sheet of green This is a very simple seaweed that reproduces itself by fragmentation, each fragment growing into a new plant. Two common kinds are found at Crane’s Beach: