TRILLIUM RECCKTA ruM. 2*1 



faces. Hence the palisade and spongy parenchyma 

 are quite distinct, and the large intercellular spaces of 

 the latter have more frequent connection with the 

 outer air through stomata. The fact that in the 

 fibre-vascular bundles of leaves the xylem is always on 

 the upper side, and the phloem on the lower, should 

 be recognized as necessitated by the relation which 

 they hold to the same regions in the stem. 



In the ovary the distribution of fibro- vascular bun- 

 dles and the relative positions of phloem and xylem 

 are most interesting and suggestive. The single bun- 

 dles in the outer walls have the phloem toward the 

 outside (the lower surface of the carpellary leaf), and 

 the xylem toward the inside. But the inner group of 

 bundles in the ovarian partitions have their arrangement 

 reversed, the phloem being on the inside (toward the 

 center of the flower) and the xylem on the outside 16 

 (see fig. 10). This is readily accounted for by the in- 

 folding of the carpellary leaves (see fig. 1 1). 



The walls of the ovary show also a region of very 

 loose spongy tissue, developed in the mesophyll of the 

 carpellary leaf, and extending into the style, the con- 

 ducting tissue, " which serves as a path of least resist- 

 ance for the penetrating pollen tubes." 18 



15 Cf. Goodale, Physiological Botany, p. 173. 



16 Goodale, Physiol. Bot , p. 172. 



