430 Prof. H. Marshall Ward. The Relations between 



living carrot, or turnip,* and the whole placed in a moist atmo- 

 sphere, &c, the hyphee do not at first enter the tissues as above de- 

 scribed, but form a dense mycelium on the surface, and branches 

 from this slowly penetrate into the interior, producing the symptoms 

 referred to. If the carrot or turnip is first submerged for half a minute 

 into boiling water, however, the hyphee plunge into the outer cells 

 (the protoplasm of which has been killed by the hot water) at once. 

 These facts are easily explained when we recognise that the hot 

 water causes plasmolysis of the cells, and escape of the sap into the 

 intercellular spaces, cell-walls, &c. ; in short, destroys the fighting 

 power of the protoplasm against the hyphse. Moreover, the latter 

 are invigorated by their saprophytic nutrition, and are able to excrete 

 such quantities of ferment that the still living cells deeper in the 

 tissues are unable to withstand the attack. 



Equally conclusive is the following experiment : — 

 A mature firm shoot of a Petunia was infected with the mycelium, 

 and the hyphse penetrated into the cortex about 1 cm., and then 

 grew no further; evidently because the cell-walls were thick, and 

 their protoplasm disposed of the poisonous zymase as fast as it 

 reached them. When the infection was made on slightly etiolated, 

 rapidly growing shoots, however, the fungus entered at once, and 

 destroyed the entire shoot off-hand. f This is explained by the 

 thinner, watery cell- walls, and the less vigorous protoplasm, more 

 acid cell-sap, and so forth, of the latter offering less resistance to the 

 zymases or poison execreted by the hyphee. 



Another excellent case is the following. During the very wet, 

 cold, and dull weather of the summer of 1888, plants suffered a good 

 deal from such diseases as we are discussing, and the white lily- 

 buds were utterly destroyed in my neighbourhood by an epidemic of 

 Botrytis,% aggravated by the low rate of transpiration, and conse- 

 quently retarded respiration and metabolism, and the diminished 

 assimilation leading to paucity of carbohydrates. The cell- walls were 

 thin and watery, the sap unduly charged with acids, &c, and the 

 protoplasm of the cells less capable of dealing with the poison emitted 

 in larger and larger quantities by the hyphee of the invading fungus. § 

 It was a very easy matter to directly infect the tissues of these lilies 

 at the time mentioned, but considerably more difficult to do so when 



* As ii rule, roots are less acid than other organs, and inflorescences more so than 

 leaves, which again are more acid than the stem (Gr. Krauss, ' Ueber die Wasserver- 

 theilung in der Pflanze, IV, Die Aciditat d. Zellsaftes,' 1885; also Warburg, loc. cit. 

 p. 116). 



+ De Bary, ' Bot. Zeitung,' 1886, col. 440—441. 



X See < Annals of Botany,' vol. 2, 1888, pp. 319—376. 



§ Warburg showed tt at the leaves of Lilium candidum contain more acid when 

 the temperature is lowered (op. cit., p. 140). 



