1915] 



DAVIS — ENZYME ACTION IN MARINE ALGAE 783 



that they cannot function as reserves. Cross, Bevan, and 

 Smith ('95) consider the pentosans as by-products of metab- 

 olism and once formed remain unalterable. Ravenna and 

 Cereser ( '09), on the other hand, in some very interesting ex- 

 periments, found that when dextrose was supplied as the sole 

 nutrient to the leaves, pentosans increased greatly, especially 

 in the light. If, however, the function of chlorophyll is in- 

 hibited, a decrease in the amount of pentosans takes place. 

 These results form the basis for their conclusion that pento- 

 sans may sometimes function as reserves. 



The origin of algal slime. — The question concerning the 

 origin of the slimy and gummy constituents of cells, whether 

 they arise through enzyme action or through other causes, 

 has provoked much discussion. There is considerable doubt 

 whether such gums can arise directly from true cellulose or 

 whether they are, at least in the case of the plant mucilages, 

 laid down as such. 



One might roughly group the plant gums into those arising 

 as a result of some external excitant, such as, for example, 

 cherry gum, acacia gum, gums of citrus, etc., and those which 

 seem to be normal constituents of the plant, as the mucilages 

 found in the epidermis of many seeds and plant organs. The 

 former arise as a result of a pathological condition ; the latter, 

 as far as we know, are normal physiological products and as 

 such are more nearly comparable to the algal slime. 



Klebs ('84), investigating slime formation in some of the 

 lower algae, particularly some of the Desmidiaceae, held that 

 it was not a conversion product of cellulose. Hauptfleisch 

 ( '88) substantiated the conclusion of Klebs, and going further, 

 states that it arises in this particular case through the activity 

 of the protoplasm, being excreted through pores. Oltmanns 

 ( '04, p. 76) illustrates very clearly the arrangement of these 

 pores. Tschirsch ('89) differentiates these slimes or muci- 

 lages into those giving a cellulose reaction and those not doing 

 so, the former having some relation perhaps to the cellulose, 

 but the latter being laid down on the cell wall as such by the 

 protoplasm. He holds the epidermal slime of Spirogyra to 

 be of this latter type, which he calls "echter Schleim." In 



