90 PROCEEDINGS OP THE AMERICAN ACADEMY 



does not seem to be connected in any way with the formation of either 

 the reproductive organs or the huirs. One might suj^pose that the 

 different zones represent successive periods of growth and rest. For 

 instance, the zonal outgrowths may represent a point where the growth 

 of the marginal cells was checked, and where, after a period of quies- 

 cence, they began growing again suddenly. What the cause of such 

 a cessation and subsequent resumption of growth might be, is a question 

 which cannot be decided without carefully observing the conditions of 

 growth of the plant. It is to be regretted that the plant could not have 

 been studied in the living state ; but that was of course imjiossible, 

 owing to the remoteness of its habitat. 



Of the hairs in Zonaria variegata two kinds may be distinguished, 

 those which occur in tufts scattered irregularly over the frond, and 

 those which are rhizoid-like in their nature, and are found chiefly near 

 the base on the under side of the frond, not arising in compact tufts 

 like the others. The hairs in the tufts are always unbranched, and 

 are composed of long cylindrical cells placed end to end. Tliey de- 

 velop from the elongation of a group of cortical cells, and are in the 

 young stages protected by a covering which subsequently breaks away, 

 as described by Naegeli in the case of Padina Pavonia. The rhizoid- 

 like hairs resemble those which develop in tufts in that they are out- 

 growths of the cortical cells, but they differ in that they are scattered 

 irregularly over a considerable area. They may also be distinguished 

 by the greater length of their component cells and by the fact that 

 they are branched (Fig. 5). While they are usually developed only 

 near the base of the frond, they may occur to a limited extent any- 

 where on its under surface. 



The reproductive bodies which I found on the frond of Zonaria 

 variegata, although no division into four parts was seen, were presuma- 

 bly young tetraspores. As Bornet has remarked,* however, it is very 

 difficult to distinguish the tetraspores from the so called oogonia unless 

 the division of the former into four parts is seen ; and although appar- 

 ently not a difficult matter to detect the four tetraspores in living mate- 

 rial, in dried or alcoholic material the mother cell of the tetraspores 

 often appears to be undivided. They arise from the enlargement and 

 division of groups of epidermal cells, and are protected in their young 

 stages by a covering like that found in the case of the hairs. They 

 were not at all definitely arranged, being scattered irregularly in 

 patches between the overlapping zones. 



* Etudes Phycologiques. 



