304 GYNO-DICECIOUS PLANTS. CHAP. TIL 



We may now consider the probable means by which 

 so many of the Labiatae have been separated into two 

 forms, and the advantages thus gained. H. Muller* 

 supposes that originally some individuals varied so as 

 to produce more conspicuous flowers ; and that insects 

 habitually visited these first, and then dusted with 

 their pollen visited and fertilised the less conspicuous 

 flowers. The production of pollen by the latter plants 

 would thus be rendered superfluous, and it would be 

 advantageous to the species that their stamens should 

 abort, so as to save useless expenditure. They would 

 thus be converted into females. But another view may 

 be suggested : as the production of a large supply of 

 seeds evidently is of high importance to many plants, 

 and as we have seen in the three foregoing cases 

 that the females produce many more seeds than the 

 hermaphrodites, increased fertility seems to me the 

 more probable cause of the formation and separation of 

 the two forms. From the data above given it follows 

 that ten plants of Tliymus serpyllum, if half consisted 

 of hermaphrodites and half of females, would yield 

 seeds compared with ten hermaphrodite plants in the 

 ratio of 100 to 72. Under similar circumstances the 

 ratio with ftatureia hortensis (subject to the doubt from 

 the self-fertilisation of the hermaphrodite) would be as 

 100 to 60. Whether the two forms originated in cer- 

 tain individuals varying and producing more seed than 

 usual, and consequently producing less pollen ; or in 

 the stamens of certain individuals tending from some 

 unknown cause to abort, and consequently producing 

 more seed, it is impossible to decide; but in either 

 case, if the tendency to the increased production of 

 seed were steadily favoured, the result would be tho 



1 l>ic Befruchtung der Blumen,' pp. 319, 326. 



