1254 A TEXTBOOK OF THEORETICAL BOTANY 



We may contrast with pollination in the Ranunculaceae the state of 

 affairs in the Gramineae, where wind-pollination is the rule. The grasses 

 certainly do not represent a primitive type of Monocotyledon and the 

 adoption of wind-pollination is therefore probably secondary. Their 

 floral structure is both reduced and specialized and they have either no 

 perianths or only vestigial ones, but there can be no question that among 

 them this supposedly primitive mode of pollination is highly successful, 

 as is testified by their numbers and their cosmopolitan distribution. 



We have remarked that the majority of flowers are cross-pollinated. 

 Where flowers are unisexual this is naturally inevitable, but most herma- 

 phrodite flowers show arrangements which favour cross-pollination and 

 either prevent self-pollination, or at least greatly reduce it. Considering 

 the proximity of anthers and stigmas in most hermaphrodite flowers, and 

 the ease with which self-pollination could be brought about in such flowers, 

 the avoidance of it in nature struck early observers and suggested that it 

 might carry with it something like the drawbacks of inbreeding among 

 animals. Consequently it was not surprising that Charles Darwin was able 

 to show from his experiments, published in 1876 as " The Eflect of Cross 

 and Self Fertilization in the Vegetable Kingdom ", that cross-pollination 

 produces ; (a) more seed (b), heavier seed, and (c) better germination capacity, 

 than does self-pollination. 



We have shown, in the previous chapter, that there is reason for regard- 

 ing the unisexual condition in flowers as derived from the hermaphrodite 

 condition, rather than the reverse. If this be so, we may regard the unisexual 

 state as the extreme term of the trend towards ensuring cross-pollination. 

 This does not imply that self-pollination is the more primitive of the two. 

 Separation of the sexes is the rule among lower plants, and among higher 

 plants the hermaphrodite condition is only to be found, Angiosperms 

 apart, in some of the higher Cycadophyta. If the Angiosperms originated 

 with a hermaphrodite constitution, they started with a handicap in regard 

 to self-pollination, the need to minimize which may have been an important 

 cause of their multifarious variation. These are speculative matters, but not 

 without interest. 



It must be borne in mind that there are some plants which are habitually 

 self-pollinated and which have therefore become homozygous, without 

 apparently suffering any penalty. Some of these types are among the Grasses 

 and they may be widely successful, but despite the appearance of success, 

 the genie impoverishment which their condition implies must limit their 

 capabilities, as it leaves them dependent on chance mutations for the 

 appearance of any heritable variations (see also Pedkularis, p. 1324). 



The need for pollination, as a preliminary to seed and fruit production, 

 has been known from very early times and the ceremonial pollination of the 

 Date Palms was carried out as a religious act by Assyrian kings. In spite 

 of the long experience of cultivators with certain crop plants, no idea of the 

 universality of pollination in flowers found a place in botanical science until 

 it was propounded by Thomas Millington towards the end of the seven- 



