155 



A section through a leaf-tip on which yellow vesicles 

 are found (PL II figs. 9 and 10.), shows that thèse vesicles 

 are caused by hyportrophy of cells of the spongy paren- 

 chyma which hâve thcro entirely lost their tubular shape 

 and among which spécimens are found, measuring 91 by 

 109 fi, 100 by 73 (x, 100 by 113 /w etc. Among the cells, 

 constituting the vesicle, some are always found which in 

 unstained préparations are conspicuous by their wall being 

 more or less swollen and brown (with x in fig. 9, the 

 somewhat darker drawn walls in the middle part of fig. 

 10). In préparations, treated with acid fuchsin and methyl 

 green, the wall of thèse cells is blue, those of the other 

 cells red. Applying the usual reactions we flnd that thèse 

 walls hâve become suberized. Also of the palissade paren- 

 chyma some cells may hâve become larger, but always in 

 a small degree. (cf. fig. 10). 



While in the vesicles themselves the process goes a 

 little further still on account of partition walls forming 

 in some of the enlarged cells, whose walls hâve not become 

 suberized, also the région, surrounding the vesicles, evi- 

 dently answering to a stimulus, proceeding from them, 

 begins to undergo similar changes. Macroscopically we 

 detect this by the more or less yellow tint, assumed by 

 the vicinity of the vesicles. A microscopical examination 

 of the section (PL II, fig. 11) shows that now also outside 

 the vesicles the cells of the spongy parenchyma are 

 hypertrophical. As with the formation of the visicles the 

 chlorophyl is disorganised in the hypertrophical cells. 



At this stage no function of importance may be ascribed 

 yet to the cells belonging to the palissade parenchyma. 



In most préparations now already the peculiar behaviour 

 is noticed of those spongy parenchyma cells which border 

 immediately on the palissade parenchyma. While the other 

 cells of the spongy parenchyma swell as evenly as possible 

 in ail directions, those which lie immediately below the 



