﻿Douglas Spruce, Pseudotsuga mucroxata 01 



constant feature of stipular outgrowths* May not the leaves in 

 conifers be regarded as exceptional, however, on account of their 

 peculiarities in the distribution of the vascular tissue, and their 

 manner of growth ? If, however, the use of the term stipule en- 

 tails the idea that the causes underlying the origin of the lateral 

 expansion of the bracts in Pseudotsuga and the true stipule of the 

 Angiosperms are the same, we have here a more serious objection 

 and one which cannot be put .away without further study. In 

 Abies such an expansion of the bracts takes place, and certain fea- 

 tures in the cones of this genus and of Pseudotsuga indicate that 

 the pressure 'of the scales upon the bracts may account for it. 

 This explanation is suggested by a consideration of the maturin 

 cones of Pseudotsuga. During the growth of the cone after fer- 

 tilization, the pressure of the scales upon the bracts, which con- 

 tinue to grow at their bases, increases and they become narrower 

 and more constricted wherever this increased pressure is brought 

 to bear upon them. This is, of course, in their lower parts which 



are not exserted. 



As to the function of these bracts it may be said that, while 

 they are undoubtedly assimilative to some degree both before and 

 after anthesis, they serve more especially as guides to lead the 

 pollen to the micropyles during pollination. In this regard, 

 therefore, they are far different from the stipules of angiosperms. 



The transverse section of the upper or laminar portion of a 

 bract shows that the bracts conform to the leaves in their plan of 

 structure, but do not develop any supporting cells in the interior. 

 This is correlated with the fact that the bracts do not support 

 themselves in the more or less horizontal position in which the 

 ordinary leaves are placed, but simply hang down. The paren- 

 chyma, moreover, consists of spherical cells and there is no well 

 defined palisade tissue nor stellate cells. 



A similar section taken through the stipular region shows the 

 same features, and shows in addition the character of the lateral 

 expansion, which consists of a thin extension of the spherical 

 parenchyma cells bounded above and below by the epidermis. 

 The endoderm is here but poorly developeo\while in the lamina 



"The Nature and Origin of Stipule*," A. A.Tyler, Ann. N. Y. Acad. Set, 



*o: 1-49. 1897. 



