34 



A TEXT-BOOK OF BOTANY. 



cal outgrowths developed on the surface of the fronds. This 

 form is found more abundantly north of Boston than south, but, 

 as Chondrus is collected at Cohasset, Scituate, and other towns 

 south of Boston, it is not seen in commerce in this country. 



Rhodymenia, or Irish Dulce, is one of the commonest red 

 sea-weeds in the North Atlantic Ocean, usually growing with Fucus, 

 Laminaria, and other Algae between tide marks and extending 

 into deep water. The fronds are purplish-red, flat, membra- 







Fig. 17. Gigartina mamillosa. a red sea-weed closely related to Chondrus crispus. 

 showing a dichotomously branching thallus and bearing at the upper part numerous cylin- 

 drical outgrowths in which the fruit bodies (sporangia) are found. — After Kutzing. 



naceous, 15 to 30 cm. in length, irregularly cleft, palmate or 

 dichotomous, the margin often being marked with numerous 

 small divisions. The sporangia occur in scattered patches im- 

 mersed in the cortical tissues of the frond. It is a common article 

 of commerce and is said to possess anthelmintic properties. 



Agar-agar is derived from several of the marine x\lg3e grow- 

 ing along the eastern coast of Asia, notably species of Gracilaria, 

 Gelidium, and Gloiopeltis. It is a mucilaginous substance which 

 is extracted from the sea-weeds, and is used extensively as a 



