38 PLANT LIFE. 



phycophixin (brown). The chloroplasts exist chiefly in the 

 cortex, which is, therelbre, the food-making tissue (see •[ 230), 

 while the internal tissues are used for storage of reserve food. 



46. Intercalary zones of growth. — Some of the brown 

 seaweeds, instead of growing at the ti]), grow in a zone at 

 the base of the flatter jiart of the thallus, just above the round 

 stalk. Such growth is called inlercalary growth. There can 

 be no single initial cell, but at least a zone of initials. 



Some species grow- to great lengtlis. One Australian species 

 is said to attain a Icngtli of 200-300 meters. Still others 

 have the form of a tree, tlie stalk-like portion representing 

 the trunk, with a crown of flattened, frond-like branches 

 above (fig. 46). 



The thallus in tlie "gulf-weed," or " sea-grape "* (fig. 

 47), is still further ciifferentiated into rounded, stem-like parts 

 and flattened, leaf-like ones. The bladders are berry-like 

 enlargements in the middle of short, rounded branches, and 

 the form is strikingly like that of a small herb. 



* 'Ihis plant is of interest, also, because from its scientilic name, Sar- 

 gasstim, is derived the name of tliat region in the North Atlantic, in the 

 loop of the Gulf Stream, the .Sargasso Sea, where the plants accumulate 

 after being torn off the tropical shores on which various species grow. 



