( 24 ) 



summit ; sometimes a branch becomes elongated and branched in its 

 turn Uke the main stem, but generally the branches are quite simple, 

 generally much smaller, but occasionally much more developed than the 

 main stem, which is at times short and slender, or thick and truncated. 

 Sometimes all the parts are long, slender, cylindrical, smooth and even 

 on the surftice ; at other times, as in var. /3, the stem and branches 

 are greatly thickened about or a little below the middle, more or less 

 compressed, -UTinkled, often more or less twisted in a regular spiral. 

 Structure, when young, composed internally of an exceedingly lax net- 

 work of hyaline, anastomosing, jointed filaments ; joints contracted in 

 the middle, four to six times longer than broad, extremely lax in the 

 centre, more dense outward ; the centi-al portion disappearing with the 

 growth of the plant, the outer portion forming a very lax lining to the 

 now tubular frond, and from the outer filaments arising the vertical, 

 dichotomous, jointed filaments, that constitute the main body of the 

 frond. These are lax at first, but by rapid and repeated subdivision 

 become denser at the circumference, forming a close stratum of moni- 

 liform cells. Substance soft and lubricous, adhering very closely to 

 paper. Favellae formed by the metamorphosis of the dichotomous 

 filaments, and j)laced at their base, containing numerous angular spores. 

 Tetraspores cruciate, similarly formed and situate. 



This cui'ious plant is a very common inhabitant of our tide-pools all 

 round the coast. The variety /3 seems to grow in greatest luxuriance, 

 and to exhibit its peculiar characteristics in estuaries where the water is 

 somewhat brackish. In such places it often reaches a large size, but the 

 smooth cylindrical fronds may be observed growing from the same tufts as 

 the wrinkled ones ; the larger ones being generally of a paler colour. 



The appearance and disapj)earance of sea- weeds is often very curious. 

 We have gathered this plant in abundance in the beginning of June, 

 and in the same pools by the middle of the month not a vestige 

 could be found, although the weather had been perfectly calm all the 

 time. We have often observed the same circimistance with respect to 

 other Algae, and to such an extent as to add vastly to the interest which 

 the marine botanist will derive from visiting frequently even the same 

 part of the coast. 



EXPLANATION OF PLATE LXXIV. 



Fig. 1. — Dumontia Jiliformis, natural size. 



2.— Filaments of the periphery with tetraspore. 



3. — Tetraspores. 



4. — Filaments with a favella. 



5. — Spores from same. 



6. — Section of variety /8. 



7. — Section of normal state. All magnified. 



