DISPERSION OF POLLEN BY THE WIND. 141 



invariably commences after the anther has assumed a pendent position. The 

 filajments and anthers are joined together by a slender connective, and the tissue 

 of this connective is, as it were, articulated so that the anther is capable of 

 turning freely without becoming detached (a condition termed versatile). Hence 

 under any circumstances the requisite position can be assumed; that is to say, 

 the at first uppermost ends of the anthers can be made to hang down whether 

 they are on pendent, or on horizontal, or even on erect filaments. When this 

 inversion has been accomplished the anther-lobes open along the sutural lines 

 already referred to. The slits only gape open for a short distance from that 

 extremity of the anther which is now lowest. This partial opening is in some 

 measure dependent on the further circumstance that at the dehiscent portion 

 the two anther-lobes separate from one another and curve round in opposite 

 directions, as is shown in fig. 231^. The significance of this inflection lies in 

 the fact that the powdery pollen is prevented from falling out of the loculi the 

 moment the slits are formed. For the curved ends of the anther-lobes assume 

 the shape of little hollow boats in which the pollen may rest for quite a long- 

 time if the air is still (fig. 231^). It is not till a gust of wind sets the anthers 

 swinging that the pollen -dust is blown away in the form of a small cloud 

 (fig. 231"^, to the right). On the first occasion only the tiny heap pertaining 

 to the dehiscent extremity of the anther is removed, but this is immediately 

 replaced by fresh pollen pouring down from the upper indehiscent portion of 

 the anther. This new supply naturally has no long time to wait, but is blown 

 away by the very next gust. The process may be repeated several times, and 

 generally does not cease until there is no longer any pollen left. When the 

 anthers are quite emptied they drop off the filaments in the form of dry husks. 

 Usually, however, this detachment of the anthers does not take place till several 

 hours after pollination, and in the majority of Grasses, plants which have 

 flowered in the early morning or during the day still have their empty anthers 

 hanging to the spikes or panicles, as the case may be, at sunset. 



The changes preceding pollination are much more markedly dependent 

 on the weather in Grasses than in other plants. The temperature and hygro- 

 scopic condition of the air in particular play an important part. Rain and low 

 temperatures may delay the splitting asunder of the glumes and the extrusion 

 and dehiscence of the anthers not merely for hours, but for days. A very dry 

 atmosphere accompanied by a high temperature also has the eflect of retarding 

 the processes above described. The most favourable conditions for pollination 

 in the case of most Grasses prevail in the early morning at an hour when there 

 is still some dew lying on the meadows, when the first rays of sunshine fall 

 obliquely upon the flowers, and the temperature is rising gently and a light 

 breeze sets the spikes and panicles in motion. Under such external conditions 

 as these the phenomena of flowering and pollination are accomplished with 

 astonishing rapidity. In some Grasses an observer may see the glumes relax 

 and spring open, the stamens grow out, the anthers open and the pollen scat- 



