IB JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



finds expression in its incapacity to utilise all the starch at 

 its disposal. But this point will be raised again in the 

 general discussion under Section Y. Here I will simply point 

 out that, although this appears to be the case, directly a 

 leaf is actually affected by fog, the plant, by a special effort 

 perhaps, is able to dissolve its starch and to transfer it to the 

 stem. The leaves belonging to some twenty genera of plants 

 which had fallen under the influence of fog were preserved in 

 alcohol at once. They were carefully examined for starch by 

 means of sections, which were treated with potash for six hours, 

 then neutralised in dilute acetic acid and mounted in a solution 

 of iodine dissolved in potassic iodide. In only one case 

 (Schlegelia) was starch found, except in the guard-cells of the 

 stomata. In Schlegelia parasitica the starch was not in the 

 chlorophyll-corpuscles, but in some loose parenchyma accom- 

 panying the vascular bundles. It was found only in the lower 

 third of the leaf. The leaf had evidently fallen before it had 

 been entirely withdrawn. The presence of starch in the guard- 

 cells of fallen leaves seems to be universal, whatever the cause 

 of death may have been. It is a normal phenomenon demon- 

 strated years ago by Sachs, and probably due to the lack of 

 continuity of the protoplasm between these cells and the adjacent 

 ones of the epidermis. In those cases — especially type 1, and to 

 a less degree type 2 — in which matters of nutritive value remain 

 behind (i.e. as compared with the residues remaining in the cells 

 when the leaf dies naturally) the actual cause of detention may 

 be the plasmolysis. Assuming that the protoplasm were not at 

 once killed, its withdrawal from the cell-membranes would offer 

 a serious impediment to the out-passage of proteids and the like. 

 I consider that a very interesting line for further investigation 

 arises here. 



How are the Leaves attacked ? 



I stated on p. 14 that I thought it probable that in most 

 cases, which I distinguished from the mere corrosions of an acid 

 deposit upon the epidermis, the impurities of fog had access to 

 the intercellular spaces of the leaf, and that the living substance 

 of the leaf was attacked from within. In the case of thin, 

 delicate, oncuticularised leaves this cannot be proved. All the 

 layers of the leaf, as in Centropogon or Ilcteroccntrou, indicate 



