ALGAE. PHAEOSPOREAE. 69 



not however very distinctly marked off from the older tissue. In the rind are gum- 

 passages of similar structure to those in the Cycadeae. The part of the stem outside 

 the central medulla consists of looser tissue in which the cells form filiform branches 

 resembling the hyphae of fungi ; these grow in between the cells of the medulla, the 

 cell-walls of which swell up strongly, and force them apart. 



The growing-point is intercalary, as in the Ectocarpeae, lying at the point where 

 the stalk passes into the leaf-life expansion ; here is found a meristem, where the 

 increase of the stem in length takes place. In some Laminarieae, as L. flexicaulis, 

 the flat expansion at the end of the stalk, which is of great length and breadth, is 

 permanent and continues to enlarge as long as the individual lives. In other species 

 the stem is perennial, but the leaf-like expansion is thrown off every year (compare the 

 description of Acetabularia above). Fig. 43 is a representation of L. Cloustont, which is 

 on the point of throwing off its old lamina ; this is shaded in the figure and marked b b. 

 The growing-point is at e. From it has proceeded the broad plate between e and tf b', 

 the new lamina. This plate is divided by longitudinal slits into separate strips in a 

 palmate manner, as the old lamina was. Such strips are already separated at d, and 

 a new slit is being formed at c. Other species (L. saccharine^ for instance, which is 

 found in the Atlantic and other seas, as L. Cloustont is in the North Sea) have a very 

 long and undivided expansion. In Agarum this is pierced by many roundish holes, and 

 still more remarkable formations are seen in the great Laminarias of the southern 

 hemisphere, as Macrocystis^- and Lessonia^ whose appearance cannot well be explained 

 without figures. The only known organs of propagation are unilocular sporangia; 

 a sexual process has not hitherto been observed, but must no doubt occur. 



d. A sexual process has been certainly ascertained in the CUTLERIACEAE 2 , which are 

 really directly allied to the Ectocarpeae, and are removed from them here only because 

 in their mode of fertilisation they afford a transition to the Fucaceae. This little group 

 consists of two genera, Cutleria and Zanardinia ; the development of the former only 

 will be briefly sketched here, that of the latter must be alluded to only occasionally and 

 for comparison's sake. The thallus of Cutleria is a broad flat fleshy many-layered 

 expansion split at the margin into simple narrow segments. The growing-point is at 

 the margin, but not on its outer edge. We get a good idea of this, if we suppose the 

 margin of the thallus of a Cutleria to be composed of a number of filaments of 

 Ectocarpus lying beside and in some places over one another, each of which has its 

 own intercalary growing-point, and also lateral branches beneath it. But behind the 

 margin the filaments grow together into a solid tissue, the origin of which from the 

 coalescence of separate elements is no longer discernible. The sexual organs in 

 Cutleria are dioeciously disposed, and antheridia are formed on some plants, oogonia 

 on others ; in Zanardinia they occur together on the same plant. Antheridia and 

 oogonia form groups on the surface of the thallus and are branches of short cell- 

 filaments which spring from the cells of the rind. Both take the form of 

 plurilocular sporangia ; but the compartments are smaller in the male than in the 

 female. In each compartment of the female sporangium (oogonium} a large female 

 swarm-cell is formed, in each compartment of the male sporangium (antheridium) two 

 small male ones. Both the kinds of swarm-cells are set at liberty by the opening of the 

 compartments of the sporangia ; but the female cells soon come to rest, and assume 

 the round form of an oosphere, in which a hyaline spot occupies the position of the 

 colourless beak of the female swarm-cell and is the receptive-spot. A new Cutleria 

 does not proceed directly from the oospore ; this developes first of all into a row 

 of cells and from that into a club-shaped mass of cell-tissue, on which eventually 



1 Wille, H., Zur Anat. von Macrocystis luxuriant, Hook. fil. et Harv. (Bot. Ztg. 1884, 801). 



2 Reinke, Entwicklungsgesch. Untersuch. iiber die Cutleriaceen des Golfes von Neapel (Nova 

 Acta Leop. Car., Bd. XL.)- Falkenberg, Die Befruchtung u. d. Generationswechsel von Cutleria 

 (Mittheil. aus der zool. Station zu Neapel, Bd. I. 1876.) [Jan czewski, Note sur la fecondation du 

 Cutleria adspersa et les affinitesdes Cutleriees (Ann. Sc. Nat. 7 ser. XVI. 1883).] 



