1885.] G. M. Giles—On the Protliallus o/Padina pavonia. 75 



question. There are many points in connection with these bodies that 

 require clearing up, but these can hardly be solved without continuous 

 observation of the living plant. Like all surf-line weeds, Fadina jpavonia 

 requires a very free supply of oxygen, and the conditions necessary for 

 observing it in, if I may so s^^eak, captivity are wanting on board ship ; 

 so that the solution of these points must, I fear, be reserved for other 

 observers more favourably situated. Assuming, however, that the body 

 which has just been described is really the protliallus of this weed, it 

 would render it extremely probable that all algse producing " spores " of 

 but one kind go through some such cycle of changes; and a very large 

 field of investigation appears in prospective as to the determination of 

 the protliallus of each species. Some no doubt have been described as 

 distinct species of algo3, as, assuming their existence, they can hardly 

 have been entirely overlooked up to now. 



Explanation of the Plates. 

 Plate IV. 



Fig. 1. Padina pavonia, nat. size. The sori are disposed in concentric lines 

 consisting of a structureless flattened indusial sac and a number of pear-shaped 

 sporanges. Tufts of paranemata disposed along their sides give to the sori a woolly 

 appearance. 



2. Vertical section of frond through a sorus showing sporanges and parane- 

 mata, X 200. 



Plate V. 



Fig. 1. Prothallus of Padina pavonia, natural size. 



„ 2. The same, x 10. 



„ 3. Transverse section of same, x 20. 



„ 4. Portion of the section shewing male tubes in oblique section, x 300. 



„ 5. Male mother-cell containing daughter-cells producing red-pigmented 

 rods, X 400. 



„ 6. Portion of the section shewing a female tube in transverse sec- 

 tion, X 300. 



„ 7. Adeniform tissue of lower surface of the prothallus containing 

 " hedgehog" cells in its meshes, x 300. 



„ 8. One of the " hedgehog " cells more carefully drawn, x 500. 



