v.] THE DEAD NETTLE. 155 



Lamium amplexicaule, in addition to the normal 

 flowers, also produces cleistogamous ones (Figs. 36, 

 37), which appear in the early spring and again in 

 autumn. 



In this genus it would appear, as already men- 

 tioned, that the pistil matures as early as the stamens, 

 and that cross-fertilisation is obtained by the relative 

 position of the stigma, which, as will be seen in the 

 figure, hangs down slightly below the stamens, so 

 that a bee bearing pollen on its back from a pre- 

 vious visit to another flower would touch the pistil 

 and transfer to it some of this pollen, before coming 

 in contact with the stamens. 



In other species belonging to the same great group 

 (Labiates) cross-fertilisation is secured by the fact 

 that the stamens come to maturity, shed their pollen, 

 and are shrivelled up, before the stigma is mature. 

 The genus Sal via was described by Sprengel, and 

 more recently by Hildebrand and Ogle (Pop. Sci. Rev. 

 July, 1869). Fig. 112 represents a young flower of 

 Salvia officinalis in which the stamens (/) are mature, 

 but not the stigma (/), which, moreover, from its 

 position is untouched by bees visiting the flower, 

 as shown in Fig. 113. The anthers, as they shed 

 their pollen, gradually shrivel up ; while on the other 

 hand the pistil increases in length and curves down- 

 wards, until it assumes the position shown in Fig. 

 1 14 st, where, as is evident, it must come in contact 

 with any bee visiting the flower, and would touch 

 just that part of the back on which pollen would be 

 deposited by a younger flower. In this manner self- 

 fertilisation is effectually provided against. There 



