8i4 



PHENOMENA OF SEXUAL REPRODUCTION. 



the mechanical contrivance for preventing self-fertihsation and for ensuring crossing^ is 

 extremely beautiful and easy to understand. Fig. 459 represents a flower of S.pratensis 

 seen from the side ; at « is the two-lipped stigma in a receptive condition ; and indicated 

 by a dotted line inside the upper lip of the corolla is the position of one of the two sta- 

 mens. If a pin is inserted into the tube of the corolla in the direction of the arrow, the 

 two stamens spring out, as indicated at a ; if a humble-bee inserts its proboscis in order 

 to obtain the honey, the open anthers strike the back of the insect, and some of the 

 pollen adheres to a particular part ; when the bee places itself in the same position in 



Fig. 459.— ^a/z'zVr fratensis : a corolla with stigmas 7i and fertile anther-lobes a ; B stamens removed from corolla. 



another flower, the pollen is rubbed off its back on to the stigma. The cause of the 

 stamen springing out in this way is made sufficiently clear in Fig. 459 B. This shows the 

 short true filamentsyy which adhere by their bases to the sides of the corolla-tube, and 

 bear at their upper end the long connective c x, which oscillates readily about its point 

 of attachment. Only the upper longer and slender arm of each connective c bears an 

 anther-lobe a, the lower shorter arm x is without an anther, and is applied to that of the 

 other stamen in such a manner that the two form together a kind of arm-chair. When 

 the proboscis of the bee in search of honey penetrates the flower in the direction of 



Fig. i,(>o. — Viola tricolor: A longitudinal section through the flower (natural size) ; B the ovary fertilised and swollen ; 

 the filaments have been ruptured and the anthers drawn up by the growth of the ovary ; C the stigma with its orifice o and 

 lip //, on the style gr (magnified) ; / sepals, Is prolonged base of the sepals, c petals, cs spur of the inferior petals or 

 nectary; fs appendages of the two inferior Stamens projecting into the spur, which secrete the nectar, a the anthers, 

 11 stigma, V bracts; D horizontal section through the ovary with the three placenta; sp and ovules sK\ E horizontal 

 section through an unripe anther. 



the arrow, the lower arm of the connective is pressed down, and the upper arm c is 

 made to move forward, and thus to strike the back of the insect. 



In the pansy {Viola tricolor) we have quite a different contrivance for preventing the 

 possibility of self-fertilisation. In Fig. 460, A and B, is shown the position and arrange- 

 ment of the parts of the flower. The cavity of the flower enclosed by the petals is 

 completely filled up by the anthers and ovary, with the exception of the tubular spur of 



^ For further details, see HildeLrand, Jahrb. fiir wiss. Bot. vol. IV, 1S65, p. i. 



