PROTECTION OF POLLEN. 115 



then reserved for another destiny which we shall have to consider more 

 carefully later on. In any case the pollen adherent to the projecting end of the 

 style, near the mouth of the tube composed of the connate anthers, must be 

 protected before nightfall, when there will be condensation of dew, or in case of 

 rain being imminent. This protection is, in fact, afforded to each floret by the 

 ligule of the adjoining corolla, which stretches out laterally and constitutes an 

 umbrella. In the Hawkweeds (Hieracium) the ligule bends so as to form a 

 covering over the pollen to be protected (cf. figs. 222 3 and 222 5 ). In Catananche, 

 another Composite, each ligule is spread out flat whilst the sun shines, but in 

 the evening becomes concave and at the same time arches over the pollen belonging 

 to its own flower (fig. 222 6 ). We cannot here go into all the differences in detail 

 which occur in connection with this form of adaptation. We must not, however, 

 overlook the fact that in these Composites the ligules of the peripheral florets of a 

 capitulum are always much longer than those of the central florets, and that the 

 pollen of the latter shares therefore the protection from wet afforded by the 

 bending over of the outer ligules. We do not mean to say that the short ligules 

 in the middle of the capitulum are not required to take any part at all in sheltering 

 the pollen. In most instances they, too, stand up and curve over inwards, and 

 act in conjunction with the longer outer ones in preventing the entrance of water. 

 The adaptation of the flowers of Catananche is carried so far that the long ligules 

 of the peripheral florets cease to bend inwards when there is no longer any pollen 

 to protect in those florets that is to say, when the pollen has been brushed off 

 and the florets have entered into their last stage of development (cf. fig. 22 2 7 ). 

 The short ligulate florets in the central part of the capitulum must then of course 

 see to the protection of their pollen themselves. This is the reason why one sees 

 only the central ligules of old heads of Catananche arched inwards, whilst those 

 near the margin remain motionless and stand out in rays during the dewy night 

 just as they do under the noontide sun. 



The mechanism for the protection of the pollen is well worthy of notice in 

 those Composites also in which the central florets of the capitula are all tubular 

 and the peripheral florets all ligulate, and in those where the tubular florets are 

 crowded together on a round disc and encompassed by an involucre of stiff leaves 

 which resemble petals. The Marigold (Calendula) may be taken as type of the 

 first group, and the Carline Thistle (Carlina acaulis) as type of the second 

 (fig. 224). In these plants the style grows and pushes the pollen out at the top 

 of the tubular florets, just as in the case of the ligulate flowers above described 

 it was pushed up through the hollow cylinder formed by the connate anthers, 

 and above each floret a little lump of pollen is seen resting upon the free end of 

 the style. These tubular florets are, however, incapable of securing their pollen 

 against bad weather, and a division of labour is therefore in some degree instituted 

 within the limits of each capitulum, the ligulate florets or radiating marginal 

 bracts, as the case may be, which produce no pollen, being turned to account 

 for the purpose of sheltering the pollen-bearing florets of the centre. In fine 



