62 



FLORAL LEAVES 



cium consists of six stamens,, of which two have shorter filaments 

 {at) than the remaining four (am). Many members of the 

 Foxglove — and Dead' Nettle-family (figs. 

 191, 193) have flowers with four stamens, 

 ■ two of which have shorter filaments. 

 Again, in some members of the Geranium- 

 family, the flower may possess five stamens 

 with anthers, and five without. 



Dehiscence and insertion of the anther. 

 — When the anther is ripe, the pollen-sacs 

 open in such a manner as to permit the 

 escape of the pollen. Usually each anther- 

 lobe opens by one split down the line 

 which denotes the junction of the pair of 

 pollen-sacs (figs. 85 d, 86) : its dehiscence 

 is longitudinal. Occasionally the anther 

 opens by small circular holes — e.g. Potato 

 (fig. 84 pd) : this dehiscence is porous. 

 Or, finally, the anther may open by small 

 doors or valves — e.g. Barberry : this de- 

 hiscence is valvular. When an anther 

 opens on the face towards the centre 

 of the flower, its dehiscence is introrse — e.g. Violet and 

 Daisy-family ; but when it opens towards the periphery 

 of the flower, dehiscence is extrorse ; finally, when the 

 anther dehisces neither in an inward nor an outward 

 direction, but opens along the edges, the dehiscence is 

 marginal. Unfortunately the terms extrorse and introrse 

 are also employed in another sense. An anther which is 

 inserted in such a manner that its lobes and pollen-sacs 

 appear to face the centre of the flower is described as introrse : 

 when the pollen-sacs appear to face the periphery of the flower 

 the anther is extrorse; finally, there remains a third class of 

 anthers, in which two pollen-sacs face the centre of the flower, 

 and two face the periphery. Frequently the direction of 

 dehiscence corresponds with the mode of insertion of the 

 anther, but this is not invariably the case; for example, 

 though an anther with introrse dehiscence is often found to 

 be introrse in insertion, it is not always the case. 



Fig. 88. — Flower of 

 Wallflower, with calyx and 

 corolla removed : w=nec- 

 tary ; at^ flwz = stamens ; ov 

 = ovary; j= stigma- lobe. 



