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Show Vl CONTENTS. CHAPTER VII. SuMMARY OF 'l'HE HEIGHTS AND \VEIGIITS oF 'l'HE CRos ED AND SELF-FERTILISED PLANTS. Number of species and plants measured- Tables given - Preliminary remarks on the offspring of p.lants crossed by .. a fresh. stock_ Thirteen cases specially constdered- The eHec~~ of crossincr a self-fertilised plant either by another self-fertthsecl plant 0~ by an intcrcrossed plant of the old stock- Summary of the results- Preliminary remarks on the cros~ed and .selffertilised plants of the same stock- The twenty-~ix exceptwnal cases considered, in which the crossed plants chd not exceed greatly in height the self-fertili~ed- Most of th<:se c~s.l'S s.how:t not to he real exceptions to the rule that cross-fertihsat1on JS beneficial- Summary of results- Relative weights of the crossed and self-fertilised plants . . . • . . . . Page 238-2 4 CHAPTER VIII. DrFFEttENCE BETWEEN CROSSED AND SELl?-FERTILISED PLAN'rs J ~ CoNS'l'I'rU'l'IONAL VIGOUR AND IN OTIIER RESPEC'I.' • Greater consti tutio.nal vigour of crossed plants-The effects of great crowding- Competition with other kinds of plants- Self-fertilised plants more liable to premature death- Cro sed plant~ generally flower before the self-fertilised-Negative effects of int.ercrossing flowers on the same plant- Cases describe<lTransmission of the good effects of a cross to later generations -Effects of crossing plants of closely related parentageUniform colour of the flowers on plants self-fertilised during several generations and cultivated under similar conuitions. 285-311 CHAPTER IX. 'l'HE EFFECTS OF 0ROSS-FER'l'ILISATION AND SELF-FERTILISA'l'ION ON THE PRODUCTION OF SEEDS. Fertility of plants of crossed and self-fertilised parentage, both lot~ being fertilised in the same manner- Fertility of the parentplants when first crossed and self-fertili~ed and of thrir cros~ed ' CONTENTS. Vll and self-fertilised offspring when again crossed and self-fertilised -Comparison of the fertility of flower8 fertilised with their own pollen and with that from other flowers on the same plant -Self-sterile plants- Causes of self-sterility -The appearance of highly self-fertile varieties- Self-fertilisation apparently in some respects beneficial, independently of the assure<1 production of seeds- Relative weights and rates of germination of seeds from crossed and self-fertilised flowers . . J:>age 312-355 CHAPTER X. MEANS OF FERTILISATION. Sterility and fertility of plants when insects are excluded- The means by which flowers are cross-fertilised- Structures favourable to self-fertilisation- Relation between the structure and conspicuousness of flowers, the visits of insects, and the ad vantages of cross-fertilisation- The means by which flowers are fertili~ed with pollen from a distinct plant- Greater fertilising power of such pollen- Anemophilous species- Conversion of anemophilous species into entomophilous- Origin of nectarAnemopbilous plants generally have their sexes separatedConversion of diclinous into hermaphrodite flowers- Trees often have their sexes separated . . 356-414 CIIAPTER XI. 'l'HE HABITS OF INSECTS IN RELATION TO THE FERTILISATION OF FLOWERS. Insects visit the flowers of the same species as long as they canCause of this habit- Means by which bees recognise the flowers of the same species- Sudden secretion of nectar_..::.. Nectar of certain flowers unattractive to certain insects- Industry of bees, and the number of flowers visited within a short time- Perforation of the corolla by bees - Skill l:ihown in the operation- Hive-bees profit by the boles made by humble-bees -Effects of habit- The motive for perforating flowers to save time- 'Flowers growing in crowded masses chiefly perforated. 415-435 |