ZOOLOGY AND BOTANY, MIC.HOSCOPY, ETC. 483 



The starcli is not formed directly by the combination of water and 

 carbonic acid ; there are, on the contrary, manifestly a number of 

 little- known intermediate products. 



The general results of these observations may be stated to be that 

 there is no such great gap as has hitherto been supposed between the 

 formation of starch in those cells that do and in those tliat do not 

 assimilate. In those cells that do not contain chlorophyll, there are 

 special structures which produce starch, these being simply immature 

 chlorophyll-grains, which are usually transformed into chlorophyll 

 under the influence of light. On the other hand, chL^rophyll-grains 

 are not mere organs of assimilation ; in the conducting tissues and 

 recaptacles for reserve materials they exercise the same functions as 

 the starch-produoers do in the cells that do not assimilute, i. e. they 

 construct starch out of the assimilated substances conveyed to them 

 from other parts of the plant. 



Action of Frost on Evergreen Plants.* — When plant-tissues are 

 attacked by frost, ice is generally formed, not in the interior of the 

 cells, but on the surfaces of the organs, or in the intercellular spaces, 

 where indeed considerable quantities of ice may accumulate, forcing 

 back the tissue. V/hen the ice-ciystals form in the intercellular 

 spaces of green plants, a change of colour is generally observed ; 

 in place of the normal, more or less greyish, green, the parts 

 become much darker green, because the air between the green 

 cells is replaced by ice. These purts are also more transparent than 

 usual. 



In frozen leaves these changes may easily be observed, especially 

 on the under sides, where the intercellular spaces are very numerous. 

 The leaves then look as if they were injected with water, and as if 

 water had been introduced into them from without ; but really it is 

 the cells that have furnished the water to form the ice-crystals in 

 those intercellular spaces. Thus the case is not one of injection, but 

 of a phenomenon which we might designate as infiltration. If the 

 infiltrated parts thaw, and continue to live, the liquid goes back 

 from the intercellular spaces into the cells, and the normal colour 

 returns. 



Besides this infiltration, it may be observed that in various 

 plants in the frozen state their leaves hang down, as if they were 

 withered. On thawing, they resume their normal position. In some 

 few plants both of these symptoms of the frozen state of leaves very 

 quickly disappear, and the idea was suggested that both phenomena 

 are results of very special peculiarities of organization. Still, the 

 possibility remained that they are simj^ly consequences of general, bat 

 still little-known, laws, which govern the freezing and thawing of 

 plant-tissues (a matter to be determined only by more extensive 

 systematic research). 



This question has been investigated recently by Herr Moll, of 

 Utrecht. He had repeatedly noticed that, by merely touching for a 

 moment, with the finger, the infiltrated leaves of evergreen plants, 



* Nalurfuraeher, xiv. (1881). See Engl. Mech, xxxiii. (1881) pp. 7-8. 



