ECOLOGICAL 193 



differences in structural ^detail. Finally there was an appearance of 

 "monstrosities", such as dwarfs, albinos, and forms with various 

 grades of abortion in pollen and ovules. Apart from the monstrosities, 

 which may also occur among cross-pollinated plants, the reduction 

 in size, productivity, and variability was not associated with 

 unhealthiness or degeneration in the majority. What happened 

 was probably this. The inbreeding involved in the self-polUnation 

 tends to bring to light a number of recessive characters (see 

 Mendelian Inheritance), which were kept out of sight by their 

 corresponding dominants, which are more likely to be present 

 when cross-pollination is the rule. The apparent bad effects of 

 inbreeding (self-pollination) are in all probability mainly due to 

 the segregation and unmasking of recessive characters, while the 

 apparent stimulus following outbreeding (cross-pollination) is in 

 all probability mainly due to the complementary action of pooled 

 dominant factors. 



It may be regarded as certain that estabhshed self-poUination 

 does not necessarily imply loss of vigour or variability; and it should 

 be remembered that the very successful and variable hawkweeds 

 (Hieracium) are parthenogenetic ! 



DISPERSAL OF SEEDS.— It was towards the end of the Old Red 

 Sandstone Period that Seed-bearing plants emerged, and it was a 

 great step in Organic Evolution. Previously plants had multiplied 

 by spores or unicellular germs, separated in vast numbers from the 

 parent ; but now there began to be multiplication by means of seeds. 

 That is to say, what were liberated from the parent were embryo 

 plants, in a resting stage of development, but more or less well- 

 equipped; and they had been living for some time in intimate 

 union with the parent plant. The contrast between multiplication 

 by spores and multiplication by seeds was something approaching 

 or anticipating the contrast between oviparous and viviparous 

 animals. A mother salmon liberates thousands of eggs on the gravelly 

 bed of the river; contrast that with the mother otter that gives 

 birth in her retreat to a well-formed cub. So, in a broad way of 

 speaking, do sporophytes differ from spermophytes, though, as has 

 been explained elsewhere, the spermophytes are still disguised 

 sporophytes. 



A well-equipped seed's chances of life when it is sown are much 

 greater than those of a spore, but there is the disadvantage attendant 

 on a great advantage, that even the smallest seeds are large com- 

 pared with spores; and it is therefore more difficult to secure their 

 dispersal. What we seek to illustrate here is the diversity of ways in 

 which the problem of seed-scattering has been solved. 



Before doing so, let us make an elementary point clear, that for 

 purposes of dispersal the seed and the fruit, especially when small 



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