ESSENTIAL FLOKAL LEAVES. 107 



Structure. — The pistil is made up of the usual three systems 

 of tissue, but only a few of the more important details can be 

 given here. Cross-sections through one of the ovaries of larkspur 

 or columbine will show a well-marked notch on the ventral side, 

 corresponding to the ventral suture. A layer of epidermis is 

 present on the outside, which can be traced right through the 

 wall where the notch occurs, after which it becomes continuous 

 with a layer of epidermis lining the loculus. The carpel being a 

 folded leaf, we might have expected this. The outer and inner 

 epidermis correspond, in fact, to the lower and upper layers of 

 epidermis in a foliage leaf (cf. p. 64), and in a very young ovary 

 of larkspur the margins of the carpel will be found in contact, 

 but not united. It is also interesting to note that the inner epi- 

 dermis possesses stomata as well as the outer, though they appear 

 to be useless in such a position. Between the epidermic layers 

 comes the parenchymatous ground-tissue traversed by numerous 

 vascular bundles. Each margin of the carpel is swollen slightly 

 at the ventral structure, so as to form a placenta, upon which 

 a row of ovules is borne, as can be seen in a longitudinal 

 section. 



Cross-sections through a syncarpous ovary, such as that of lily, 

 hyacinth, or violet, do not show sharp boundaries between the 

 constituent carpels (cf. fig. 51). The outside is covered by a 

 continuous layer of epidermis, which does not dip inwards where 

 the carpels unite. Each loculus is lined by its own separate 

 layer of epidermis. 



The style is sometimes traversed by a pollen canal, as in lily 

 and hyacinth. This canal may oj)en to the exterior in the centre 

 of the stigma, as in pansy (fig. 51). More frequently the centre 

 of the style is occupied by a very delicate, loose, conducting tissue, 

 as, e.g., in fuchsia and evening primrose. 



The stigma is frequently provided with delicate hairs, and its 

 cells generally form minute projections or papillae at the surface. 

 They also secrete a sticky fluid when the stigma is mature. 



An Ovule (figs. 48 and 49) is a minute ovoid body, in which 

 there is an attached base or chalaza and a free apex. The base 

 is in most cases fixed to the placenta by a slender stalk, the 

 f a aide, which is traversed by a vascular bundle. The ovule is 

 covered by either one or two skins or integuments, within which 

 is a central mass of cells, the nucellus. The integuments do not 

 cover the extreme apex of the ovule, where a short canal, the 

 micropyle, is left, which leads down to the nucellus. One integu- 

 ment only is present in gymnosperms and most gamopetalous 

 dicotyledons, while there are two in nearly all monocotyledons 

 and many dicotyledons. In the latter case the inner coat, being 



