EUPHYCOPHYTA 



203 



becomes club-shaped. The lowest cell at the narrow end elongates 

 to form the first rhizoid whilst the cell at the other end divides 

 twice by two longitudinal walls at right angles to give a quadrant. 

 Further divisions result in the development of a central group of 

 cells, the primary medulla, with the cortex outside. Additional 

 rhizoids are produced and the apex of the embryo becomes flat- 

 tened and one cell produces a hair with a basal intercalary meristem. 

 Excessive growth of neighbouring cells results in the formation of 

 a terminal depression and additional hairs are produced. Next all 

 the cells of the first hair, except the basal one, disappear and the 

 basal cell becomes the three-sided apical cell. In those Fucales, e.g. 

 Fucus, where the adult condition of the apical cell is four-sided, 

 this change in the apical cell takes place quite early, the new four- 

 sided cell being cut off from the original three-sided one. The 

 pecuhar salt marsh fucoids (see p. 349) are interesting in that the 

 juvenile three-sided apical cell persists throughout life. 



Yvcaceae: Pelvetia (after the French botanist. Dr. Pelvet). Fig. 114 



The fronds in this genus have no mid-rib and are linear, com- 

 pressed or cyHndrical with irregular dichotomous branching. Air 



^ S 



Fig. 1 14 Pelvetia canaliculata. A, plant ( x f ). B, megasporangium 



(x6o). C, mature fertilized sporangitim ( x 72). ne= rejected 



nuclei. D, germinating oospores ( x 72). E, microsporangia ( x 156). 



(Aj original; B-E, after Scott.) 



