580 THE GENESIS OF NEW SPECIES. 



subordinate degree, if at all, dependent on the parent-species for their production. 

 Nay more, it would be prejudicial were one of those species to supply the pollen 

 seeing that the fertility of this hybrid is diminished thereby. We have here a case 

 of a hybrid manifesting enhanced fertility as compared with one of its parents ; for 

 Medicago falcata is one of those Papilionaceae in which autogamy is attended with 

 very small result. It has been ascertained that in cases where the flowers of that 

 species are thrown upon their own resources for pollen, out of every 30 flowers 

 only two or three fruits containing seeds capable of germination are matured. If 

 flowers of Medicago falcata are crossed with pollen belonging to another species, 

 such as Medicago sativa, a much larger number of fruits is produced, and it is 

 stated that the number of seeds is almost doubled. Medicago media usually sets 

 from six to eight pods in each raceme if the flowers depend upon their own pollen 

 for fertilization. If, however, pollen is brought to them from Medicago falcata 

 the degree of fertility is strikingly reduced; the flowers so crossed either remain 

 quite empty or develop pods whose seeds are not capable of germination. Medicago 

 media is therefore an instance of a hybrid which is actually injured by being 

 crossed with one of the parent-species, but is successfully reproduced by autogamy. 

 The upshot of all these experiments is that the results of autogamy are no difierent 

 in hybrids from what they are in species. 



We may infer from the same experiments in what way reversions of hybrids to 

 their parent-species should be regarded. Botanists possessed with the idea that 

 every hybrid was the product of some process contravening the laws of nature 

 imagined that this anomaly must be counteracted, and that this was effected by a 

 tendency existing in the hybrid's descendants to approximate sometimes to one and 

 sometimes to the other parent-species, so that in the course of a few generations 

 they would completely revert to the form of a true species. As the accounts given 

 by gardeners seemed to confirm the fact of the occurrence of such reversions, no 

 doubt was raised as to the soundness of this view. The reports of gardeners on the 

 subject were, however, founded on inaccurate observation, want of knowledge, and 

 self-deception. In former years the phenomena of pollen-transport in the case of 

 pseudo-hermaphrodite, dichogamous, and heterostyled flowers, and many other 

 things connected therewith, were not appreciated at their full value; to most 

 gardeners they were altogether unknown, and it was only in the rarest instances 

 that any measures were taken to preserve the species and hybrids reared in gardens 

 from extraneous pollen. The majority of growers had no suspicion that the fruit 

 formed on a particular cultivated hybrid might be due to the eflect of pollen con- 

 veyed by the wind or by insects from one of the parent-species flourishing in the 

 vicinity, and if they noticed that the seedlings arising from that fruit exhibited 

 characteristics approximating to either of the parent-species they were in the habit 

 of calling the phenomenon a reversion. But if a gardener takes care that the flowers 

 of a hybrid under cultivation are only supplied with pollen developed in flowers of 

 their own kind whilst that of other species is excluded, the plants which arise from 

 the seeds of the hybrid exhibit the characters of that hybrid unaltered. Thus, 



