EFFECT OF PARASITIC FUNGI ON CELL-CONTENTS. 3S 



parts, which become pale and die. This is exemplified in 

 Cronartvum asclepiadcum on the leaves of Vincetoxium, Crym- 

 nosporongium clavci.riaeformc on the quince, Uncinula accris on 

 the Norway maple, Rhytisma punctatum on Acer spicatum. 



Intermediate between these two extremes are cases where 

 the chlorophyll is retained, but in much reduced quantity. For 

 example, organs under the influence of Exoascus alni incanac or 

 Accidium elntinum, though still green, are pale in contrast to 

 those normally deep green; leaves attacked by Peronosporeae, e.g. 

 Corydalis or Anemone with Plasmopora pygmaea, and Anemone 

 with Aecidinm punetatum or Puccinia fnsca\ leaves of Cirsium 

 containing mycelium of Puccinia suaveolens ; leaves of alder 

 with Exoascus epijjJiyllus, and many others. This paler coloura- 

 tion of diseased plants is frequently an easy means of recognizing 

 them amongst the healthy ones. 



The third case is that of " mycetogenous chloranthy " or the 

 development of green colour in organs normally of some other 

 colour. Wakker has proved this in the petals and stamens of 

 Brassiea nigra and Sisymbrium p)annonicum attacked by Gystopns 

 and Peronospora. Likewise Magnus showed its existence in 

 flowers of Anemone ranunculoides with Aecidimn inmctcdum. 



The cell-sap, in some cases of hypertrophy, assumes on the 

 sunny side a rose colour ; thus in galls caused by Exobeisidijim 

 on alpine-rose and cowberry, pear-leaves with Roestelia ceincellatet 

 and Polystiejma ndyrum, catkins of alder attacked by Exoascus, 

 and galls caused by Taphrina carnea on the sweet birch. The 

 epidermal galls, due to some species of Synchytrium {S. ruhro- 

 cinctum, S. anemones, etc.), exhibit an intense carmine coloui. 

 Yellow coloration occurs, according to Wakker, in nettle, buck- 

 thorn, and many plants when frequented by Uredineae. There 

 may also be a yellow colour due to the yellow oily contents 

 of the mycelium shining through the host-tissues, as in spruce- 

 needles with Chrysomyxa ahietis. 



In considering the effect of parasitic fungi on the starch- 

 contents of the host-plant, two very distinct cases may be 

 observed. There may be, for a time, a greater accumulation 

 of starch in the attacked parts than in the normal, or the 

 parasite may dissolve any starch present and utilize it at once. 



