

SUPPLEMENT 9 



of water, salts, and also of atmospheric gases, oxygen, nitrogen, and carbon- 

 dioxide, and would regulate the entry of these in the way above mentioned. 

 This hypothesis is certainly in harmony with all the differences in permeability 

 of protoplasm that have been observed. First with regard to specific differ- 

 ences. Bacteria and Cyanophyceae allow many substances to diosmose easily 

 to which the protoplasm of other plants is impermeable ; Penicillium does not 

 permit the entry of salts of copper, which are taken up readily by the majority 

 of plants ; Beggiatoa absorbs sulphuretted hydrogen, which cannot enter 

 certain other Algae living in its neighbourhood. Moreover, variations occur in 

 the single individual, due to external or internal transformations. It is fre- 

 quently the case in experiments that the characters of the plasmatic layer 

 cannot be altogether natural ; precipitation membranes may arise, for example, 

 by contact of the protoplasm with a salt solution or even with water, and 

 under such circumstances we should be studying the characters of these mem- 

 branes and not those of one naturally formed (BERTHOLD, 1886, p. 152 ; 

 PFEFFER, Phys. I. no, note). It is thus doubtful whether in DE VRIES'S 

 experiment referred to above (p. 7 of Suppl.), and which attempted to prove the 

 impermeability of the protoplasm of beetroot to sugar, quite natural plasmatic 

 layers were under consideration or layers which had been altered by water or 

 deficiency in oxygen, or which had been freshly formed ; for it has been shown 

 that under appropriate experimental conditions sugar can very readily undergo 

 exosmosis from such store-houses of reserve (WACHTER, 1905). 



In speaking of a newly-formed plasmatic layer arising in the place of the 

 old one we must not omit to emphasize the fact that such new formations 

 have been shown to occur in certain regions of the protoplasm. It occurs, for 

 instance, in Vaucheria, on the surface of every particle of protoplasm which 

 exudes from a wound, and which rounds itself off into a sphere ; it may be 

 observed to take place, also, on every cut surface in a Myxomycete plasmodium, 

 as also in the interior of a plasmodium after the introduction of soluble foreign 

 bodies (e.g. asparagin ; PFEFFER, 1890). In conclusion, we may note, further, 

 that exosmosis and endosmosis depend not only on the characters of the proto- 

 plasm but also on those of the cell-wall, for it, too, may often render the cell 

 impermeable to certain substances, e.g. when it becomes suberised (comp. 

 KROMER, 1903). Now since suberisation may take place in a few hours after 

 wounding (APPEL, 1906), it might be possible to explain in this way the absence 

 of exosmosis of sugar in DE VRIES'S beetroot experiment. 



On the whole, therefore, it must be specially noted that recent research 

 has tended to explain the contradiction that previously existed between the 

 results of plasmolysis and experiences with reference to the nutritive necessi- 

 ties of the plant. One saw that the plants absorbed from the soil a number 

 of substances which, on the evidence of plasmolysis, could not pass through 

 the protoplasm. We now know that almost all bodies can pass through the 

 protoplasm, but that it regulates the material exchange by altering its charac- 

 ters. This knowledge certainly forces upon us the conviction that the material 

 exchange is a complicated vital phenomenon and not, as used to be thought, 

 a simple physical process. 



P. 26, 11. 19-21, for and also . . . considerable read but chiefly, and widely, 

 with the number and size of the spaces left between the soil particles : the 

 water capacity is, however, always very considerable. 



28, 1. 20, for (1748) read (1731-3) 



11. 24, 26, for 1882, p. 19 read Lectures, p. 13. 



11. 39-44, for Root-hairs are . . . which have the effect read As BUSGEN 

 (1905) has shown, different types of absorptive roots occur in trees. One 

 type (e.g. Ash) has long but sparingly-branched absorptive roots, showing no 



