762 EEPORT— 1887. 



their physiological processes present any sp?ciiil features. The species chiefly dealt 

 with are Facus vesiculosus, L. ; F. serratus, L. ; Ascophyllam nodosion, Le Jolis ; 

 F.canaliculatus, L. ; Laminnrirt Ji(/itaf,a, 'Lamom: ; and Jlimanthalia lorea, Lyngb. 

 He finds that the cell-walls possess chemical and physical properties which are 

 not met with in those of ordinary plants — although the fundamental composition is 

 that of cellulose — and 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. Experiments made to determine the quantity of water the 

 walls may contain show it to he very great. A piece of Ascojjhyllum nodosum, Le 

 Jolis, which when dried weighed 0'65 gramme, absorbed artificial sea-water until 

 the weight reached 1-56 gramme, a gain of 140 per cent. Another piece, which 

 weighed 078 gramme, increased in fresh water to 2-53 grammes, showing a gain 

 of 225 per cent. Similar experiments, made with pieces of Jlimanthalia lorea, 

 Lyngb., showed a gain ranging from 200 to 240 per cent. There is thus some 

 difference in the quantity of water that can be stored up in tlie cell- walls of different 

 species, but it is sufficiently large in all cases to prevent injury from desiccation 

 when the plants happen to be left high and dry by the falling tide. 



The function of absorption is performed, as in most aquatic plants, by the whole 

 surface. This is true both for liquids and gases. It is a significant fact that neither 

 stomata nor intercellular spaces have hitherto been met with in these plants. The 

 absence of these structures is usually correlated with tlie aquatic habit and the 

 consequent non-existence of transpiration. But in aquatic phanerogams, such as 

 Myriophyllmn, Hlppurix, Ilottonia, Niimphcca, Alisma, Toiaiiioyi'ton, and others, 

 we have a well-developed system of intercellular spaces which includes large 

 chambers filled with air. Hence the absence of these structures in the brown sea- 

 weeds can scarcely be duo to the aquatic habit alone. It ought rather, perhaps, to 

 be correlated with the ab.sence of any neces-ity for mechanical a-sistance in main- 

 taining the erect position, and may prevent transpiration when the plants are ex- 

 posed, but in any case it proves that intercellular spaces are not indispensable for 

 respiratory purposes, and that in the plants under consideration the absorption of 

 gases is performed by the superflcial cells alone. 



The absence of transpiration is a priori evidence that there is little or no move- 

 ment of wat-^r from \iAow upwards, and experiment shows positively that such is 

 the case. Water and other fluids aie readily conducted laterally from the surface 

 inwards, but not in the longitudinal direction. 



The metabolic processes of the brown sea-weeds, especially those connected with 

 assimilation, present some interesting and important features. In the first place, 

 careful search has hitherto failed to show in them any trace of starch. The follow- 

 ing species have been specially examined with respect to this point, and all agree 

 in giving only negative results : — Facus vesicidosus, L. ; F. serrnt.us, L. ; Ascophyllum 

 nodosum, Ly Jolis ; F. cini'diculatus, L. ; Halidrys siliquosa, Lyngb. ; Himanthalia 

 lorea, Lyngb. ; Lamimiria diijitata, Lamour. ; L. saccharina, Ijamour. ; Desmarestia 

 (iculeata, Lamour. ; Leathesiu tuherifomiis, Gray ; Chordaria JicKjelliformis, Ag. ; 

 Mesogloia virescens, Carm. ; Sphacelciria cirrhosa, Ag. 



But if starch is absent the proteids are present, and generally in considerable 

 quantity, showing that the constructive metabolism which gives rise to these bodies 

 — proteosynthesis, as it may be called — is tolerably active in these plants. 



_ The significance of these peculiarities is probably great, but is by no means clear. 

 Millardet has shown that the Fucacecc contain three pigments — viz., chlorophyll, 

 phycoxanthine, and phycophteine. Hansen has recently confirmed and extended 

 Millardet's observations, and finds that the chlorophyll o"f the higher plants is com- 

 posed of two constituents, a green and a yellow, the latter of which is identical with 

 the phj'coxanthine of the Fucacecc. Hence it is the presence of the jihycophpeine 

 which distinguishes the assimilating organs of the Fucacea- from those of ordinary 

 grepu plants, and which may be directly or indirectly responsible for their peculiar 

 action. 



The plastic materials being then wholly or for the most part proteinaceous, the 

 arrangements for their distribution through the plant must be adapted to their 

 chemical and physical properties. This is found to be the case. In the Fucaceee, 



