THE ANATOMY OF THE SHOOT 85 



Development of Bud Scales. — Like the stipule, the bud scale 

 or cataphyll has received relatively little attention from the onto- 

 genetic point of view, the principal references to it being con- 

 cerned with its relation to phylogeny and speculation with respect 

 to theories of recapitulation and metamorphosis. Certain generali- 

 zations can be made regarding the principal anatomical differences 

 between the bud scale and the foliage leaf, (i) Stomata are 

 reduced in number or may be entirely lacking; and, when present, 

 are more numerous on the adaxial surface of the scale than on the 

 abaxial one, which usually has a heavy cuticle, (i) There is a 

 reduction in the amount of mechanical tissue of the collenchyma- 

 tous type. (3) There is usually a reduction or complete absence of 

 palisade tissue; and the parenchymatous cells are homogeneous 

 with fewer air spaces than are found in the spongy parenchyma of 

 the foliage leaf. (4) There is a definite reduction in the amount of 

 vascular tissue, the number of xylem and phloem elements is 

 reduced, and the former are less strongly lignified. 



Considerable interest attaches to the question as to what factors 

 determine whether a foliar primordium will develop as a cata- 

 phyll or as a foliage leaf. Goebel (xi) has regarded the cataphyll 

 as developing from a foliar primordium which is arrested in its 

 developmental stages and as a result pursues a divergent ontogeny 

 leading to the differentiation of a bud scale. Objections to this 

 "transformation" theory have been raised by Schiiepp (37) and 

 Foster (15), the former showing that the character and position of 

 the meristematic tissue, and the rapidity of its maturation, are 

 important factors in determining the ultimate development of a 

 foliar primordium. Foster has suggested that there is a significant 

 periodic alternation of cataphylls and foliage leaves. He has also 

 noted differences in the character of the meristematic activity and 

 the development of the derivative cells of the bud scale as compared 

 with the foliage leaf. 



LITERATURE CITED 



I. Arber, Agnes, "On the occurrence of intrafascicular cambium in monocoty- 

 ledons." Ann. Bot. ^i: 41-45, 1917- 

 1. , "Further notes on intrafascicular cambium in monocotyledons." 



Ann. Bot. ^2: 87-89, 1918. 

 3. , "Studies on intrafascicular cambium in monocotyledons. Ill, IV." 



Ann. Bot. ^y 459-465, 191 9. 



