Jan. 1900.] BOTANICAL SOCIETY OF EDINBURGH 34;> 



as many as three being not uncommon, while, on the other 

 hand, they are frequently reduced to one. 



They are generally placed laterally, but may occasionally 

 occupy an oblique position, and may even, though but 

 rarely, be found in the median plane longitudinally above 

 or below the papilla. 



On shoots of the current year no papilLe wdiatever are 

 at first recognisable, -and they do not make their appear- 

 ance till a considerable amount of elongation has taken 

 place and the season is well advanced. Small superficial 

 elevations may then be observed on the stem, at or near 

 the base of the year's growth, and as the shoot increases in 

 age these appear at progressively higher levels, till in late 

 autumn, when growth has completely ceased, they may be 

 found within one or two internodes of the apical bud, 

 wliile those first formed at the base of the shoot have 

 already assumed the characters of second year's papillio, 

 and, like them, bear lateral lenticels. 



The relative number in which these structures appear 

 varies greatly in different plants, and even in different 

 parts of the same plant, their formation seeming to depend 

 to a considerable extent on the degree of transpiration to 

 which the branches are exposed. Plants inhabiting moist 

 situations, such as the margins of deep ditches, etc., have 

 in general their stems almost entirely covered with papilhc, 

 while individuals living in dry airy positions are, on the 

 other hand, nearly devoid of them. In the case of plants 

 growing in hedges and thickets where the surrounding- 

 vegetation supplies a considerable check to air movements 

 and thereby limits transpiration, papilke are especially 

 abundant on the protected twigs, while those which project 

 above the surrounding herbage, and are thus more exposed, 

 are comparatively free from them. Papilhe are also not 

 unfrequently found in larger numbers on the lower than 

 on the upper surface of horizontal branches growing near 

 the ground, and, as Beijerinck (2) has pointed out, wherever 

 a branch of this kind comes in contact with the soil the 

 root rudiments concealed within the papilhe on its lower 

 surface grow out into functional roots. 



Although plants growing in dry places never bear so 

 large a number of papilla? as those in moister situations, it 



