462 SUMMARY OF CURRENT RESEARCHES RELATING TO 



stratum, and which is wanting only in unicellular and endophytic alga). 

 Tho attachment is always superficial, tnc organ having no function in 

 the absorption of food-material similar to that of the root of higher 

 plants. Three types may he distinguished of this organ, viz. : — 



(1) On germinating, a single primary radicular cell is developed, 

 which primary cell may either he the sole root-organ, or may developo 

 secondary root-organs. The former case occurs only with comparatively 

 few alga> ; the simplest case is ErythrotricMa, which is attached only by 

 its slightly differentiated basal cell ; a somewhat higher degree of 

 development occurs in CEdogonium and Spirogyra adnata, and a still 

 higher in some species of Cladophora and Chsetomorpha, e. g. C. serea. In 

 most cases there are also secondary radicular filaments, formed by a 

 swelling at the basal end of a cell which developes into a filament, tho 

 growth of which is generally directed downwards. This filament may 

 consist of one or more cells, and may branch ; it may or may not be 

 separated from the parent-cell by a septum. Various special cases of 

 further development are described, such as the investing cortical fila- 

 ments of Batrachospermum. The large attachment-disc of Fucaceae is 

 formed entirely of intercellular root-filaments. 



(2) A creeping branched filament of cells is developed on germination. 

 This usually branches into a layer, from which ascending axes rise which 

 form the most conspicuous part of the alga; this may either remain 

 distinct, or may coalesce into a cushion or crust, as in Myrionema, Balfsia, 

 Lithoderma, &c. It is not improbable that all the Phaaozoosporere belong 

 to this type; but in Laminaria it undergoes so many changes in the 

 course of development as to be hardly recognizable. Sphacelaria is 

 distinguished by its erect polysiphonous shoots. 



(3) A cushion-like mass of cells is developed on germination. The 

 algaa belonging to this type are all Florideaa with distinct thalloid 

 shoots, such as Furcellaria, Plocamium, Gigartina, Chondrus, Lomen- 

 taria, &c. The organ does not here develope radicular filaments, as in 

 the two preceding types. 



Physiology of Phaeophycese.* — Mr. T. Hick has chiefly investigated 

 Fucus vesiculosus, F. serratus, F. canaliculars, Ascophyllum nodosum, 

 Laminaria digitata, and Himanthalia lorea. He has found that the cell- 

 walls possess chemical and physical properties not met with in those of 

 ordinary plants, and he concludes that these properties enable the walls 

 to act as a reservoir of water, on which the tissues may draw when the 

 plants are exposed to desiccating influences. The quantity of water 

 contained by the wall may be very great ; a piece of A. nodosum 

 which, when dried, weighed ■ 65 gramme, absorbed artificial sea-water 

 until the weight reached 1 ■ 56 gramme, or a gain of 140 per cent. ; in 

 other experiments gains of from 200 to 240 per cent, were observed. 

 The absence of stomata and intercellular spaces is usually correlated 

 with the aquatic habit and consequent non-transpiration ; it is to be 

 remembered, however, that in aquatic phanerogams there is no well- 

 developed system of intercellular spaces, and the absence in this par- 

 ticular case ought perhaps to be rather correlated with the absence of 

 any necessity for mechanical assistance in maintaining the erect position, 

 and may prevent transpiration when the plants are exposed ; in any case 

 it proves that intercellular spaces are not indispensable for respiratory 



* Rep. Brit. Assoc. Adv. Bci., 1887 (1388) pp. 761-3. 



