SCROPHULARINEAE 



167 



this species the corolla is of a pale green colour, but the inner surface of the 

 upper lip is brown and serves as a nectar-guide. The flower is so placed that 

 the entrance of rain-drops is prevented. It is about 5 mm. in diameter. Insect 

 visitors, particularly wasps, touch the stigma from below during the first stage of 

 anthesis, and the anthers during the second. The posterior fifth stamen has 

 become unnecessary, and is modified into a small black leaflet on the upper wall 

 of the corolla. Visitors are thus enabled to force their way into the flowers 

 exactly in the middle line. They hold on to the outside of the corolla with all 

 six legs, and push their heads into the entrance of the flower, pollinating those 

 in the first stage, and dusting themselves with pollen in those in the second 

 stage. It follows that when a number of flowers are visited in succession crossing 

 will always take place. 



i" c'^ I 



Fig. 286. Scrophularia nodosa^ L. (after Hertn. Miiller). (i) Flower in the first (female) stage, seen 

 directly from the front ( x 7). (2) Do., from below ( x 3^). (3) Older flower, pollinating itself, seen from 

 the side. (4-7) Stages in the reversion of the fifth stamen to the original leaf-like form (read from 7 to 4) 

 (x 12). o, calyx-lobes; b, corolla-lobes; c, stamens; d, modified fifth stamen; rf, ovary; c, style; 

 ft stigma ; /, nectary ; A, drops of nectar ; /, black leaf-like part of fifth stamen ; /6, anthers. 



The first (female) stage of anthesis lasts for two days. The anthers are at 

 this time unripe, and situated in the base of the flower on the bent filaments, 

 while the style protrudes to some extent from the corolla and its receptive stigma 

 is directed somewhat upwards. When the second (male) stage of anthesis begins, 

 the filaments straighten and the pollinated stigma withers and bends down over 

 the lower lip, its place being taken by the dehiscing anthers. Visitors (wasps), 

 as Sprengel long ago noticed, are in the habit of first sucking the upper (younger) 

 flowers of an inflorescence, working their way down to the lower (older) flowers, 

 from which it follows that the regular crossing of distinct stocks is secured. 



Should insect-visits fail the unpoUinated stigma remains receptive and retains 

 its original position, so that it gets dusted with pollen from the dehiscing anthers 

 above it, and completely effective self-pollination is thus automatically effected. 



Warnstorf describes the pollen-grains as whitish in colour, ellipsoidal, thickly 

 tuberculated, about 37 /* long and 18-21 /x broad. 



Visitors. Not only in Europe but also in North America wasps are the chief 

 visitors. It would appear, however, that such visits are not equally numerous in all 

 localities and at different seasons. In East Holstein, for example, I found the 

 flowers to be very zealously visited by wasps during the early part of their flowering 



