374 



HUTCHINSON'S POPULAR BOTANY 



FIG. 460. MEADOW CRANESBILL 



(Geranium pratense). 

 A protandrous flower. 



FIG. 461. BIRTHWORT (Aristolochia 

 clematitis). 



Section of flower showing palisade hairs and 

 essential organs. 



various causes, the chief of which are 

 the time of blossoming and the influence 

 of climate. Of these causes the latter is 

 the most important. In Southern Italy, 

 for example, the climate can develop 

 normally expanding flowers, and render 

 them fertile, so that cleistogamy is sup- 

 pressed ; whilst here in England the climate 

 is seemingly not sufficiently warm to do 

 this, and cleistogamic buds appear as com- 

 pensation. The vegetative energy comes 

 to the fore during the summer, but ex- 

 panding flowers are not produced simul- 

 taneously with it; indeed, as Henslow 

 observes, " it is not until the vegetative 

 period has ceased, and the materials are 

 remade for their development, that larger 

 flowers are again borne " that is to say, 

 " later in the year, as in November, and 

 also in the following spring." 



We come now to the second class of 

 autogamous flowers namely, those which 

 develop in the normal way, and expand 

 (or, at least, are capable of expansion) 

 at the period of maturity. This class, 

 as has already been explained, comprises 

 all self-pollinating flowers which are not 

 cleistogamic. It must not be supposed, 

 however, that self-pollinating flowers are 

 never cross-pollinated. As a matter of 

 fact, the former process is often only 

 adopted as a last resource. The various 

 species of Myosotis offer interesting illus- 

 trations of this truth. Thus the Wood 

 Scorpion-grass (M. sylvatica) is usually 

 cross-pollinated by flies ; but if no insects 

 appear, the anthers shed their pollen 

 directly upon the stigma, which lies con- 

 veniently below it (fig. 454, ). The 

 Yellow and Blue Scorpion-grass (M. ver- 

 sicolor) protrudes its stigma from the 

 flower when ready for pollination (fig. 

 454, 6) ; but if the usual agents in this 

 process bees and flies do not appear, 



