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Journal of Experimental Biology 1,445-472 (1924)
Published by Company of Biologists 1924

Sex in the Salicaceæ: and its Modification by Eriophyid Mites and other Influences

J. W. HESLOP HARRISON D.Sc., F.R.S.E.¹

¹ Armstrong College, University of Durham

1. The species of the two genera Populus and Salix are ordinarily dicious.

2. In the whole of the British Salix species and hybrids examined a preponderance of female plants, slight in the diploid forms, but great in the polyploids, was discovered.

3. In the diploids this excess, if significant, probably arises from the slower growth of pollen tubes carrying the male determining gametes.

4. In the polyploids that influence is assisted (a) by the occurrence of apomixis with thelytoky ; (b) by pseudo-fertilisation with thelytoky; (c) by circumstances arising from peculiarities marking the chromosome complexes of polyploid dicious plants.

5. Hybrid Salices, when combinations of diploid species, invariably possess males.

6. Other hybrids of which at least one parent is polyploid, are exclusively female as far as observation goes or, at best, produce but few males.

7. These latter features may arise from circumstances detailed in (4), or there may be a deliberate and permanent switch-over of the heterogametic sex as in my Lycia-Nyssia crosses.

8. Certain hybrids produce, in addition to plants of the normal male and female types, androgynous or moncious forms.

9. These are explained as arising through environmental influences temporarily switching the metabolism of a male plant over from its normal condition to that characteristic of the opposite sex.

10. If that be the correct view the switch-over must occur, with a subsequent reversal, annually.

11. In the Capreæ group intersexual florets occur.

12. Such are induced by the attacks of parasites in the form of mites of the Eriophyid group, in particular of Epitrimerus salicobius.

13. They act by effecting local changes in the metabolism of the plant.

14. The phenomenon is thus one of parasitic castration.

15. Many similar cases are known, for which, for the most part, fungi are responsible.