94 



PART I. — ORGANOGRAPHY. 



Figs. 285 and 286 represent the pistillate and staminate stages, 

 respectively, in the development of the flower of Scrophularia 

 nodosa. The nectar is secreted in the base of the tube. In the 

 younger or pistillate stage the stigma is exposed at the entrance, 

 in such a position that a visiting insect must come into contact 

 with it in order to reach the nectar; the unripe stamens are bent 

 back out of the way. In the older or stami- 

 nate stage the stigma lies withered on the 

 lip of the flower, while the four anthers, now 

 ripe, are exposed in the throat, dusting with 

 pollen the insect that visits the flower. It is 

 evident that a bee flying from an older to a 

 younger flower must necessarily effect the 

 cross-fertilization of the latter. 



Fig. 284. 



Fig. 285. 



Fig. 286. 



Fig. 284. — Diagram of the inflorescence of Arum maculatum. The spathe is contracted 

 near its middle, and the passage-way obstructed by stiff hairs which point downward. 

 These, being flexible at their base, permit the ingress, but not the egress, of insects. The 

 pistillate flowers are clustered at a, on the base of the spadix, while the staminate flowers 

 are above at b. The former mature first, and alter the pollen is shed, the hairs wither, per- 

 mitting the pollen-dusted insects to escape. 



Figs. 28s and 286 represent the pistillate and staminate stages, respectively, of the 

 flower of Scrophularia nodosa. When the flower first opens, the stigma is mature, and in 

 the way of a visiting insect : after this has withered, the stamens curve upward, and the 

 now ripened anthers occupy a position similar to that previously occupied by the stigma. 



(3) By the prepotency of foreign pollen. It has already been 

 stated that in some cases pollen from the same flower is entirely 

 ineffective. This has been proved to be the case with Lobelia 

 fulgens, Verbascum nigrum, Primula verticillata, and some other 

 plants. 



