igoo-i.] 



Effects of Water on Foliage Leaves. 



327 



FIG. 12. 

 Section through tobacco leaf " spot." O, natural condition ; P, ring ; 

 Q, dead part of spot ; C, chloroplasts ; Int., intercellular spaces ; A, 

 towards centre of spot. 



Sumatra leaves examined were affected also with a disease similar to 

 the " Mosaic disease," and to " calico." 



Now as to the internal effect of the spraying with caustic, the writer 

 has found that the tissue undergoes some changes of importance in the 

 vicinity of the spot. 

 (See Fig. 12, sec- 

 tion perpendicular 

 to the leaf surface). 

 It appears that the 

 caustic alkali kills 

 the chloroplast and 

 the protoplasm in 

 the cells where 

 the spot becomes 

 whitish ; and that 

 on the darker green 

 ring bordering the 

 light spot, the cells 

 become larger and 

 the chlorophyll 

 bodies more numerous, especially in the palisade cells. There they are 

 found very abundantly along the sides of the palisade cells, which have 

 increased in length very considerably. The guard cells in the ring are 

 well filled with protoplasm and chloroplasts, more so than in the 

 ordinary guard cells of the leaf (see illustrations in Fig. 13). The 

 stomata in the ring present therefore a different appearance in surface 

 view from both the spot and the ordinary tissue. We notice also that 

 the leaf is much thicker and denser in this ring, and that the chloroplasts 

 are larger and more numerous. In the spongy parenchyma there is 

 some enlargement due to the expanded cells and to the increased area 

 of intercellular spaces. In the spot itself the protoplasm was dead 

 exceedingly pale, and much shrunken. It is quite possible that there is 

 a stimulus to growth produced by the caustic solution used. If this be 

 the case it would increase the activity of the protoplasm in the ring 

 immediately surrounding the part that was dead, and consequently 

 produce more numerous and larger chloroplasts. It has been shown by 

 Griffon, Ewart, Mayer and others, that potassiumi nitrate and potassium, 

 carbonate affected the chloroplasts in some way resulting in increased 

 dimensions and in general in a deeper green colour of the leaves. 

 Griffon shows, too, that it is only the palisade cells that are affected. 

 The writer has found that in the case of Nicotiana and Ampelopsis both 



