i. Expanded Contracted „ , , . 



CONTRACTION IN THE SEA ANEMONE 



When disturbed, the animal greatly reduces its surface by repeatedly contracting 

 until it resembles a wart on a rock 



Seasonal Change As the autumn advances, the soil becomes drier as 

 well as cooler. Fewer root hairs are now formed. The movement of water 

 out of the leaves is reduced. Evaporation continues, however, so long as 

 there is water in the cells. If the roots do not absorb enough to compensate 

 for the loss of water, the live cells of the plant must suffer injury. The leaf 

 cells are the first to be affected. The shedding of leaves seems to be related 

 to the water factor, as well as to the temperature factor, which we usually 

 associate with the change of seasons. This has been determined experi- 

 mentally. The loss of the leaves prevents the complete drying up of the 

 plant, and it also prevents the freezing of live cells (see illustration, p. 91). 

 We may properly think of the fall of leaves as adaptive. 



Life in a Tide Pool Organisms living along the seashore withstand 

 drying when exposed to air and beating by waves when submerged. The 

 seaweeds are tough and gelatinous, and often ribbonlike, offering little re- 

 sistance to the water currents. Sea anemones, although consisting largely of 

 water, have a firm outer membrane. Many of the animals secrete hard 

 shells. These protect the soft bodies against the rushing water, enemies and 

 drying. The mussels and barnacles close their shells while the tide is out. 

 Clams draw in their siphons, sea anemones draw in their waving tentacles, 

 snails close their horny trap doors, tube worms cover their burrows, and 

 crabs move with the water or remain in pools left by the receding tide. All 

 these water animals of this most exciting of environments lie low until the 

 next tide surrounds them with water, permitting them to resume their 

 search for food (see illustration, p. 579). 



92 



