BY MAR.TORIK ISABEL COLLINS. '2i).^ 



that tlie secretion of resin in S. crassifoHah primarily concerned 

 with bud-protection. 



Tlie secretion is still mobile upon the X'oung leaves outside the 

 bud, but since no new glands are being formed to keep pace with 

 the increase of leaf-surface, it becomes spread out over a greater 

 area and, consequently, more attenuated. The thickness of the 

 film of secretion varies in different parts of the same leaf, in 

 leaves of different age, and in diffeient plants. It often reaches 

 a thickness nearly twice the height of the glands, i.e., ab.mt 

 7G/X. (PI. xxviii., fig. 3). 



In the older leaves, the glands lose their activity, the secretion 

 becomes less mobile, and, in drying up, oacks along radiating 

 lines. Tt is at this stage that 

 the leaves present a lacquered 

 appearance. The glands, being- 

 no longer functional, cease to 

 grow, whilst the neigh homing 

 epidermal cells enlarge consider- 

 ably, and, as a result, the glands 

 ultimately appear to be sunken 

 (Text-fig. 3). The dried secre- 

 tion falls off" when the leaf 









reaches its succulent condition, Text-fi-.8.-Sunken, olandular hair in 



,, . 1 p TIT '^ mature leaf: ( xoRO). 



small patches, oi negligible 



quantity, being restricted to the region of the glands. 



The Development of the Stomata. 



Tt is obvious that any stomata which are present on the young 

 leaf coated w^ith its sticky secretion, cannot be functional. Tn 

 correlation with the rapid growth of the leaf-area, new stomata 

 are continually being formed. Thus, in a section parallel to the 

 surface of a young leaf, all stages in development of the stomata 

 may be studied, as well as a small percentage of stomata which 

 have already reached maturity (Text-fig. 4). 



Solereder (4, Vol. ii., pp. 1079-1080), wlien classifying stomata, 

 refers the Goodeniacete to two groups; (1) where there are no 

 subsidiary cells, and ('2) where subsidiary cells are formed par- 



18 



