ii6 A TEXTBOOK OF THEORETICAL BOTANY 



Only one family, the Cutleriaceae, is included in this order, and it contains 

 only two well-known genera of which we shall consider one, Cutleria. 



Cutleria multifida 



This Brow^n Alga occurs somewhat rarely around the British coasts 

 below low-tide mark, and, though apparently widely distributed, the plants are 

 usually found isolated. The male and female plants vary with the locality, 

 so that it is difficult to find any feature whereby the sexes can be distinguished 

 clearly from one another. 



These plants are attached to the rock on which they grow by a small 

 holdfast (Fig. 97). The thallus is thin and irregularly branched, the branches 



Fig. 97. — Cutleria multifida. Form of the entire sexual plant. 



varying much in width and frequency. Each branch terminates in a collection 

 of filaments of cells of varying length (Fig. 98), as described above. In 

 section the thallus is seen to be composed of large central parenchymatous 

 cells surrounded by several layers of much smaller cells, which contain the 

 pigments and form the assimilatory tissue of the plant. In addition to the 

 terminal filaments or hairs, tufts of similar hairs may be developed upon 

 the whole surface of the thallus. 



The Male Gametangium 



The male gametangia occur over the whole surface of the plant either 

 in small or large clusters (Fig. 99), usually in association with the hairs. 

 Both the hairs and the gametangia arise from superficial cells of the thallus. 

 The cell grows out and divides to give a stalk-cell below and the gametangium 

 above. Further divisions of the stalk-cell may occur so that a filament is 



