PLATE XVH.— SWEET VIOLET (Viola odorata) and PANSY (Viola Tricolor). 



The Vagrant odour of the one and the brilliant colouration of the other have rendered these flowers universal favourites but to the 

 botanist they have an additional charm in the beautiful mechanical arrangement of parts for ensuring cross-fertilisation— that is, the trans- 

 ference of the pollen from one flower to the stigma of another. 



As there are many other flowers with equally remarkable contrivances, it may prove interesting and instructive to ask ourselves and 

 answer for ourselves some of those questions which this very flower— the Sweet Violet— suggested to the mind of Sprengel who was 

 one of the first during the last century, to perceive the relations between flowers and insects. After examining the flower in order to 

 understand the position and arrangement of the different parts, he asked himself, What is the meaning of all this? and proceeded to 

 write down questions and answers similar to the following: — 



i. Why does the flower bend over?—'Yo protect the honey from rain, and to place the stamens so that the pollen will fall 

 into the space between the ovary and the free end of the stamens. 



2. Why has the corolla a spur?— To make room for the appendages of the Anthers, and to hold the nectar they 



secrete. 



3. Why is the loiuer petal expanded '?— -To serve as an alighting place for insects. 



4. Why have some of the anthers appendages 1 — To secrete nectar. 



5. Why is the base of the style bent and thin /—To enable the insect readily to bend it, as if straight it would be more 



difficult to bend 



6. Why is the pollen more pmvdery than usual?— To fall out of the anther more readily into the box formed by the 



membranous connectives. 



The object of the whole contrivance is evidently to get an interchange of pollen through the agency of insects— the honey, the colour, 

 and the smell all being so many inducements to attract them. The insect on alighting crawls between the style and the petal to reach 

 the nectar. In so doing it comes in contact with the stigma and leaves there any pollen about its head brought from another flower. 

 At the same time it bends the flexible style which moves the ovary, thus pressing back the anthers surrounding the ovary, and tapping 

 the pollen-box, as it were. As the anthers slightly overlap, this motion is communicated all round, and the pollen collecting in the 

 lower anthers will be jerked out by the necessary wagging of their appendages. The converging spoon-shaped connectives (Fig. 7) 

 regulate the distribution of the pollen on the insect's head, so that when it visits the next flower, the bulk of the pollen will be left upon 

 the open mouth of the stigma ready to receive it The lower lip of the stigma will clearly prevent the insect, as it withdraws its head, 

 from leaving any of the flower's own pollen, since the lip will close and none will stick. 



The Sweet Violet may be found in shady woods as early as February, but it may be purchased much earlier. 

 Fig". 1. Leaf of Pansy — Stipules, large and leafy. 

 Figs. 2 and 3. Vertical section of Pansy and of Sweet Violet 



Bracts, minute, near bend of flower-stalk in Pansy, about middle of flower-stalk in Sweet Violet 



Sepals, attached to receptacle so as to leave posterior ends, free. 



Petals, of different size and shape; the lowest the largest and prolonged into a spur. 



Stamens, surrounding the ovary, with little membranous orange tips, and the two lower anthers with appendages 



projecting into the spur. 

 Carpels, consisting of swollen Ovary, bent Style, and hollow Stigma, with the opening directed downwards. 

 Diagram. — Calyx, of five free Sepals, unequal in size. 

 Corolla, of five free Petals, unequal in size. 



Andrcecium, of five free Stamens, with large curved anthers overlapping one another. 

 Gynoecium, of three united Carpels. 



Fig". 4. Bract with indications of stipules. 



Fig. 5. Sepal with auricles representing stipules. 



Fig. 6. Petals — two lateral with a brush of hairs, and lower with double brush and spur. 



Fig. 7. Stamen with very short Filament, anther-lobes opening inwards and connective forming a large scoop. 



Fig. 8. Gyncecium with swollen Ovary, bent Style, and hollow Stigma. 



Fig. 9. Ovary composed of three carpels, united by their in-turned edges, which bear the Ovules. Here there is a single chamber 



and the ovules are attached to the wall of the ovary, so that the placentation is said to be parietal. 

 Fig. 10. In Narcissus the Ovule was shown on the eve of fertilisation, here — in Viola — it is shown directly after fertilisation. 

 The pollen-tube has spread out on the Embryo-sac and, by virtue of some influence conveyed by the pollen-tube to the embryo-cell 

 through the synergida, fertilisation has been effected and an Embryo formed 



The contents of the embryo-sac also break up into a number of Endosperm cells by a process of free-cell formation. 

 It may be noted that, whereas in Narcissus only a single layer of cells formed the apex of the Nucellus, here there are several 

 layers. 



Figs. 11 and 12. Fruit, a Capsule splitting up into three valves along what corresponds to the midrib of each carpellary leaf. 

 Fig. 13. Seed taken between finger and thumb may be readily halved. 



Embryo, at the attached end of seed 



Endosperm, abundant 



CLASSIFICATION. 

 Class. — Dicotyledon. 

 Division. — Polypetalse. 

 Sub-division. — Thalamiflorse. 

 Order. — Violacese. 



Leaves, stipulate. 



Flowers, irregular. 



Stamen with Connectives produced beyond Anthers. 



Placentation, parietal. 



Fruit, a three-valved capsule. 

 Genus. — Only one British genus, Viola. 



