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Show 314 CLEISTOGAMIC FLOWERS. CHAP. VIII. The :first point that strikes us in considering this list of 55 genera, is that they are very widely distributed in the vegetable series. They are more common in the family of the Leguminosre than in any other, and next in order in that of the Acanthacere and Malpighiacece. A large number, · but not all the species, of certain genera, as of Oxalis and Viola, bear cleistogamic as well as ordinary flowers. A second point which deserves notice is that a considerable proportion of the genera produce more or l~ss irregular flowers ; this is the case with about 32 out of the 55 genera, but to this subject I shall recur. I formerly made many observations on cleistogamic flowers, but only a few of the1n are worth giving, since the appearance of an admirable paper by Hugo von Mohl,* whose examination was in so1ne respects much more complete than mine. His paper includes also an interesting history of our knowledge on tho subject. Viola canina.-The calyx of the cleistogamic flowers differs in no respect from that of the perfect ones. The petals are reduced to :five minute scales; . the lower one, which represents the lower lip, is considerably larger than the others, but with no trace of the spur-like nectary ; its margins are smooth, whilst those of the other four scale-like petals are papillose. D. Muller of Upsala says that in the specimens which he observed the petals were completely aborted.t The stamens are very small, and only the two lower ones are provided with anthers, which do not cohere together as in the perfect flowers. The anthers are minute, with the two cells or loculi remarkably distinct; they contain very little pollen in comparison with those of the perfect * 'Bot. Zeitung,' 1863, p. 309- 28. t Ibid. 1857, p. 730. This paper contains the first full .an~ satisfactory account of any cleisto gamic flower. CHAP. VIII. VIOLA. 315 flowers. The connective expands into a membranous hood-like shield which projects above the anther-cells. These two lower stamens have no vestige of the curious appendages which secrete nectar in the perfect flowers. The three other stamens are destitute of anthers and have broader :filaments, with their terminal membranous expansions flatter or not so hood-like as those of the two antheriferous stamens. ~rhe pollen-grains have remarkably thin transparent coats; when exposed to the air they shrivel up quickly ; when placed in water they swell, and are then ~U:-6-~ of an inch in diameter, and therefore of smaller size than the ordinary pollengrains similarly treated, which have a diameter. of 1-/ 0t}0 1 of an inch. In the cleistogamic flowers, the pollen-grains, as far as I could see, never naturally fall out of the anther-cells, but emit their tubes through a pore at the upper end. I was able to trace the tubes from the grains some way down the stigma. The pistil is very short, with the style hooked, so that its extremity, which is a little enlarged or funnel-shaped and represents the stigma, is directed downwards, being covered by the two membranous expansions of the antheriferous stamens. It is remarkable that there is an open passage from the enlarged funnel-shaped extremity to within the ovarium; this was evident as slight pressure caused a bubble of air, which had b~en drawn in by some accident, to travel freely from one en.d to th~ other : a similar passage was observed by ~!Chalet 1n V. alba. The pistil therefore differs conSldera~ ly. from that of the perfect flower ; for in the l~tter It IS much longer, and straight with the exceptiOn of the rectangularly bent stigma ; nor is it perforated by an open passage. The ordinary or perfect flowers have been said by some authors never to produce capsules; but this is an |