APPENDIX A 



533 



first, and those right and left successively later. Each flower is strongly 

 zygomorphic, with its median plane vertical (Fig. 438). It consists of : 

 Calyx, sepals 5, gamosepalous, inferior, odd sepal posterior. 

 Corolla, petals 5, gamopetalous, inferior; strongly two-lipped. One large 

 petal forms the anterior lower lip, two smaller petals guard the entrance to 

 the tube laterally, the upper lip forms a hood, composed of two obli(iuely 

 posterior petals. The corolla is easily removed in one piece, its tube is narrow 

 below, but widens upwards. 



Androecium, stamens 4, epipetalous. The fifth posterior stamen is absent, 

 its place being inconveniently behind the style. The anthers, of unequal 

 length, and opening downwards, lie below the hood of the corolla. In this 

 Family sometimes the outer, sometimes the inner pair are the longer. 



Gynoecium, carpels 2, syncarpous, superior, antero-posterior ; style elon- 

 gated ; stigma two-lipped, lying between the pairs of anthers, with lobes 

 widely divergent, the anterior lobe directed downwards. The ovary 4-partite, 

 with one anatropous ovule in each. It is really bilocular, with two ovules 

 in each loculus ; but it becomes " falsely " quadrilocular by intrusion of a 

 septum between each pair of ovules. Nectaries are found at the anterior 

 base of the ovary. The nectar accumulates in the narrow lower part of the 

 corolla-tube, protected by a ring of hairs which grow inwards from the tube 

 of the corolla just above the ovary. 



Fruit, four dry nutlets, two being derived from each carpel. They remain 

 till shed, enclosed by the persistent calyx. 



Pollination is by bees, which alight on the lower lip of the corolla and insert 

 the proboscis into the tube. The bee's body fills the space between the upper 

 and lower lips, so that its back presses against the stamens and stigma. The 

 anterior lobe of the stigma projects further downwards than the stamens, so 

 that it first touches the back of the bee, receiving pollen if he has brought an}' 

 from another flower. He then receives pollen from the anthers which open 

 downwards. The flower is homogamous, that is, the stigma is receptive at the 

 time when the pollen is shed. Self-pollination is therefore possible, but there 

 is a high probability of cross-pollination. 



(41) The Dead Nettle is highly specialised, and deposits the pollen on a 

 limited area of the insect's body ; but a still higher degree of specialisation is 

 seen in Salvia pratensis, or other species. The plan of the flower is the same as 

 in Lamium, but, as the mechanism is more precise, sufficient probability of 

 pollination can be secured with greater economy of pollen than in other Labi- 

 atae (Fig. 439). Only the two obliquely anterior stamens are matured, the 

 posterior are represented by minute staminodes, or are quite abortive. The 

 anthers of the two well-developed stamens have the " connectives " between 

 the anther-lobes elongated, so that they are separated about half an inch. 

 Each anther is affixed midway on the short stout filament of the stamen by 

 a flexible joint, so as to be able to move like the lever of an Egyptian well. 

 One of the lobes is directed forwards, and this develops normal pollen ; 

 the other is directed backwards and develops as a sterile knob. This is so 

 placed as to block the entrance to the corolla-tube, while the fertile lobe rests 

 under the hood of the corolla. The flower is strongly protandrous, the 

 style being hidden, and the stigma-lobes appressed at the time of shedding 

 of the pollen. 



