OCR Text |
Show Vlll CONTENTS. CHAPTER XII. GENERAL HESULTS. Oross-fert.i h. sat.w n vro,.. ed t0. be beneficial and self-fertilisation in- ' . h · 1 . . . s- AI 1 ied species differ greatly m the means by. w 1 c l .] UflOUf t'l' tl'on I·s cavoured and self-f erti' l'I Sa t'I On avoi( 1 >d cross- er t - 1 1sa 1: 1 1 The benefits and evils of the two processes depend ~n t 18 c cgree of differentiation in the sexual elements~ T~e evJl efTect . not due to the combination of morbid tendenmes In th~ parentsNature of 'the conditions to whic? plants are subJected whe~ THE EFFECTS OF CROSS AND SELF-FERTILISATION. CHAPTER I. iNTRODUCTORY REMARKS. Various means which favour or determine the cross-fertilisation of plants-Benefits derived from cross-fertilisation-Self-fertilisation favourable to the propagation of the species-Brief history of the subject-Object of the experiments, and the manner in which they were tried-Statistical value of the measurements-The experiments carried on during several successive generations-Nature of the relationship of the plants in the later generations-Uniformity of the conditions to which the plants were subjected-Some apparent and some real causes of error-Amount of pollen employed- Arrangement of the work-Importance of the conclusions. THERE is weighty and abundant evidence that the flowers of most kinds of plants are constructed so as to be occasionally or habitually cross-fertilised by pollen from another flower, produced either by the same plant, or generally, as we shall hereafter see reason to believe, by a distinct plant. Cross-fertilisation is sometimes ensured by the sexes being separated, and in a large number of cases by the pollen ~nd stig1na of the same flower . being matured at different times. Such plants are called dichogamous, and have been divided into two sub-classes: proterandrous species, B |