248 



KXOWLLDGE cS: SCIENTIFIC NEWS. 



[October, 1905. 



SeaL^veeds : 



A Holida-y Pa.per for Field 

 BotaLHists. 



By U.wiD W. Bevax, Scarborough l-.N. Society. 



III. -The Green Seaweeds. 



The Green Scawec'cls — last yroup of all that ends this 

 strange, eventful history — the group that lends bright- 

 ness and cheerfulness to the rocky pools — are closely 

 allied to the .Algae of the pond and the ditch. In fact, 

 some genera {Conferva, Vaucheria, and others) have 

 representatives in both waters. 



.All lovers of fresh-water .Alga? know these plants , 

 Conferva, with its simple, unbranched row of cells, 

 Tauclieria, with its branching filament of one large 

 multi-nucleate cell. TTie green are the lowliest 

 of the seaweeds. True, some plants of the red 

 and the brown groups are equally simple in build. 

 There is practically no difference, except colour. 

 between the red Callithamnion, the brcicn tctocarpus 

 (a flufTy, yellow, much-branched plant, two inches high 

 or more) and the green Cladoplwra (the common "sea 

 moss"). In each case the filament is a simple row of 

 cells ; in each case several cells of the filament bear a 

 branch filament, and this branching is repeated again 

 and again (Fig. i shows the three plants in the order 



?< 60 



named). But the green .seaweeds never attain to 

 the complexity of structure which is seen in most of the 

 brown and the red— the Wrack and the Chilocladia, 

 to take two plants haphazard. Ulva, the .Sea Lettuce, 

 the queen of the green seaweeds, is ,1 mere double 

 sheet of cells, every t>ne like its neighl«»ur ; Eiitvro- 

 morfJia, the " sea grass," is the same thing, but is 

 narrow and hollow — hence the name. Tlie two layers 

 of cells arc only in contact at the edges, so that the 



frond is a closed tube. Ulva and Enteronn rpha are 

 shown in Fig. 2. 



Moreover, it may be repeated that the difference 

 between the three tribes lies in the reproductive pro- 

 cess. So that, although the three filamentous plants 

 mentioned above are buUt alike, we find lelrasforcs in 

 Callithamnion, tiiale and female elements in Ectociirpus, 

 while the " sea moss " has its own special method of 

 reproduction — a process which, once seen, can never 

 be forgotten. Let us turn, then, to the family arrange- 

 ments of the green seaweeds. 



If the Sea Lettuce is gathered in summer, and a bit 

 cut out with scissors and placed in a drop of sea water 

 under the microscope, the protoplasm in .some of the 

 cells is often seen to be divided into, perhaps, a dozen 

 rounded portions (Fig. 3). These are the Zoospores. 



^'}o^ 



riir. 2. F'K- 3- 



■J'hcy are destined to be discharged, to swim away by 

 a pair of cilia, and to grow at once into new L'lvas. 

 There is no union of male and female. I'Lach spore 

 is fully endowed with the power of germination. 



But to sec this wonderful sight under the best con- 

 ditions, the plant to study is the common sea moss, 

 Cladoplwra rupestris (not a moss at all), which has 

 comparatively enormous cells. Fresh, young, light 

 green fronds should be selected, and a low power 

 shows that .some of the large, oblong cells have their 

 protoplasm split up into many .scores of spores. If we 

 are lucky (or, r.ither, patient), we may see slight rest- 

 less movements in the mass ; after a while they begin 

 to slowly slide about amongst each other, till at last 

 the whole cell becomes a .scene of wild and feverish 

 excitement. The spores are all now in motion, 

 Inirrying hither and thither, pushing, jostling, in their 

 .attempts to liiul a way out (I'ig. (a). In the cntl, a 

 linv, r(nn)(l jxirc appears :il the upper end r)f the cell 

 (I''ig. 4b), and f>ut they .-dl rush one by one into the 

 microscopic <K-ean, put out their cilia, and start off to 

 see life <>i\ lluir own :iccount. .After a while tliey settle 

 down, flraw In fhrir cilia, become round — llicy were 

 pear-shaped l)efr)re- .ind begin the serious business of 

 life ; thus bringing to an end one of the most fascinat- 

 in'^ spectacles that the botanist can ever hope to gaze 



