126 



BOTANY 



evolution of the sexual cells that is found in certain groups of 

 Chlorophyceae. Thus in Ectocarpus (Fig. 95) the gametes are 

 entirely similar ; in Cutleria (Fig. 100) both gametes are motile, but 

 Qne is much larger than the other, while in Fucus (Fig. 104) there 

 is still greater difference in size, and the egg-cell is not ciliated. 



The zygote developed from the union of the gametes grows at 

 once into a new plant. The Phaeophycese, never being exposed to 

 complete desiccation or to great changes of temperature, do not need 

 to develop resting-spores, such as characterize most of the fresh- 

 water Chlorophycese. The Phaeophycese are divided into two orders, 

 Phseosporese and Cyclosporese. 



B 



Order I. Phaeosporeae 



Ectocarpaceas. The family Ectocarpaceae include the simplest of the Phaeo- 

 sporeae. Of these the genera Ectocarpus and Pylaiella are perhaps the best 

 known. The plant-body in these genera consists of extensively branching fila- 

 ments, which are sometimes prostrate and creeping, but more commonly are 

 erect. The chromatophores are either disks or somewhat irregular bands in 

 which are imbedded conspicuous pyrenoids. 



The plants branch extensively, the cells at the ends of the branches being 

 often tapering. Cell-division is most active in the basal part of the branches, 

 where the cells are usually shorter. In some of the larger forms, slender 

 branches grow downward from the base of the lateral branches and form an 



imperfect cortex over the larger cells. 



Sphacelariaceae. In the Sphace- 

 lariaceae the growth is apical, the apical 

 cell being extremely large, and may 

 even show the beginning of the lateral 

 branches before any actual division has 

 taken place (Fig. 96). In the segments 

 cut off from the apical cell longitudinal 

 as well as transverse walls may be 

 formed, so that the plant-body is no 

 longer a simple cell-row as in Ecto- 

 carpus. 



Laminariaceae. The common- 

 est and largest of all the Phae- 

 ophycese are the Laminariacese, 

 or Kelps. They are common on 

 rocky coasts in all the cooler 

 seas, and reach an extraordinary 

 development upon our own Pa- 

 cific coast, where a number of 

 peculiar genera occur. In the 

 Atlantic the various species of 

 Laminaria are the common repre- 

 sentatives of the family ; but in the Pacific, in addition to Laminaria, 



T* 



FIG. 97. A, Egreyia Menziesii, young 

 plant, natural size; r, holdfast. B, 

 older plant with young leaves, I. 



