274 I5R- J- W. HESLOP HARRISON ON 



appear for their existence. Their development in Viola spp., 

 Oxalis acetosella, Lamium atnplexicatde and, to a less extent, 

 Drosera rotundifolia and D. atiglica is quite understandable. 

 With the rapid growth of the surrounding vegetation in spring 

 these species run grave risks of being overwhelmed and thus 

 prevented from receiving the necessary insects. To avoid 

 this contingency this very specialised method of self-fertilisation 

 has been evolved. No such fate seems to threaten Rosa 

 omissa, so that the discovery of a considerable number of 

 cleistogamous flowers in that microgene occasioned great 

 surprise. In general structure these were quite comparable 

 with similar flowers of Viola hirta. 



Their ovate lanceolate sepals were perfectly normal, but 

 the involute petals, of the usual shape when straightened out, 

 were reduced in dimensions to 8 mm. by 4 mm. In colour, 

 they were greenish white. Otherwise, both the male and the 

 female organs were quite ordinary. Most significantly, the 

 amount of fully developed pollen attained the surprising 

 figure of 100 per cent. — a contrast with the normal flowers of 

 the same bush which yielded 70 per cent, good grains. 



Apomixis. 



The defective nature of the pollen in many rose microgenes 

 seemed, at first sight, to constitute a very eff^ective barrier to 

 their reproducing their kind, and therefore stimulated enquiries 

 as to how the affected forms did so. To this end bushes 

 known to have produced very defective pollen were marked in 

 July and visited in September. Without exception, these 

 individuals then bore, if possible, a greater supply of hips 

 than their companions. Further, in one instance, a Rosa 

 rubiginosa, the plant grew five miles from another member of 

 the genus. Only one explanation seemed to account satis- 

 factorily for the observed facts, and that was that in Rosa 

 some form of apomixis was prevalent. 



To put this to tlie proof, in the following season certain 

 blossoms on each of the shrubs transferred to the garden were 

 deprived of their stamens (care being taken to remove those 



