744 THE FLORAL STEM. 



palustre, and numerous species of clover. In the Alsike Clover (Trifolium 

 hybridum) growing abundantly in marshy meadows, the older flowers not only 

 sink down in order to give the place best adapted to insect visits to the younger 

 ones, but their corollas turn a beautiful red colour, contrasting vividly with the 

 white of the younger flowers. The contrast is visible at a great distance and serves 

 to attract insects. In the curled inflorescences of the Comfrey, Forget-me-not, and 

 Viper's Bugloss (Symphytum, Myosotis, Echium), and many other Boraginese, the 

 inflorescence may be seen to unfold and fix itself, so that the flowers in turn are 

 placed in the position in which they are best seen by and most accessible to flying 

 insects; meanwhile the older flowers, whose time is over, and to which insect- visits 

 are of no further use, move out of the way of those which have just opened, and 

 always choose their position so as not to obstruct the entrance to the new flowers 

 of the same inflorescence. In this process not only the flower-stalk but the rachis 

 of the whole inflorescence takes part, and it is interesting to observe how even 

 widely distant parts of the stem are sympathetically affected, so to speak, and how 

 all the different parts of the system of axes are extended, raised, depressed, and 

 curved exactly as required for the purpose of affording the most favourable position 

 to each flower in turn. 



The most remarkable thing of all, however, is that under certain conditions, 

 which only occur exceptionally, the most favourable position for the flowers is 

 striven after and obtained by means of curvatures produced in the stem in places 

 where, in the ordinary course of things, such changes would not have occurred. 

 When the Wood Forget-me-not, Larkspur, Monkshood, Adenostyles, the Willow 

 Herb (Myostis silvatica, Delphinium elatum, Aconitum variegatum, Adenostyles 

 alpina, Epildbium angustifolium), and numerous other undershrubs whose stiff, 

 erect stems are terminated by a group of brilliantly-coloured flowers adapted to 

 insect-visits, are pressed down and extended on the ground shortly before the 

 unfolding of the flowers by some unusual occurrence, so that the normally erect 

 inflorescence lies on the soil, the stem will be seen to form a bend below the 

 inflorescence, as it is no longer capable of raising up the whole length, and the 

 portion bearing the flowers will be elevated until it again becomes erect, and its 

 flowers are again placed in a position favourable to insect-visits. This curvature is 

 no ordinary phenomenon of growth, for the portion of the stem forming the bend 

 has already ceased growing, and the curvature does not extend to the rachis of 

 the inflorescence, but takes place below it, being strictly localized there; the rachis 

 itself, which is raised up, always remaining straight. Finally, no kind of stimulus 

 can be shown to affect the internodes in which the bend is formed. Contact with 

 the soil and illumination from above act just in the same way on it as on the 

 internodes above and below it. No external causes whatever can be assigned to 

 this knee-shaped bending, and only this much is certain the bending could not 

 take place at a spot better suited to the purpose of restoring the flowers once 

 more to a favourable position. 



The flowers of more than an eighth part of all flowering plants are grouped 



