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Show 28 IPOMCEA PURPUREA. CHAP. u. CHAPTER II. CoN VOL vuLACElE. ipomrea purpurea, comparison of the height and fertility of the crossed and self-fertilised plants during ten successive generations ·-Greater constitutional vigour of the crossed plants-The effects on the offspring of crossing different flowers on the same plant, instead of crossing di::;tinct individuals-The effects of a cross with a fresh stock-The descendants of the self-fertilised plant named Hero-Summary on tht- growth, vigour, and fertility of the successive crossed and self-fertilised ~enerations-Small amount of pollen in the anthers of the self-fertilised plants of the later generations, and the sterility of their first-produced flowers-Uniform colour of the flowers produced by the self-fertilised plants-The advantage from a cross between two distinct plants depends on their differing in constitution. A PLANT of Ipomcea purpurea, or as it is often called in England the convolvulus Jllajor, a native of South America, grew in my greenhouse. Ten flowers on this · plant were fertilised with pollen from the same flower ; and ten other flowers on the same plant were crossed with pollen from a distinct plaut. The fertilisation of the flowers with their own pollen was superfluous, as this convolvulus is highly self-fertile; but I acted in this manner to make the experiments correspond in all respects. Whilst the flowers are young the _ stigma projects beyond the anthers; and it might have been thought that it could not be fertilised without the aid of humble-bees, which often visit the flowers; but as the flower grows older the stamens increase in length, and their anthers brush against the stigma, which thus CHAP. II. CROSSED AND SELF-FERTILISED PLANTS. 29 bre cetihv es some pollen. Th e num b er of seed d h.Ytt le.e crossed and self-fertirl se d fl. owers d1. fsf eprreod nveeeryd maCnnro~srs ed and self-fertilised . were _allowed to germin~~ds obtamed in the above as pairs germinated at the sa t~ on damp sand, and as often manner described in the I t mde u~e they were planted in the two po t s. Fi·v e pairs were nt hr o uctwn on th · . 1 ' e opposite sides of seeds, whether or not in a stat~so~ ante~; a~d all the remaining the opposite sides of a th. d germmatwn, were planted on both sides were here gre~~l pot, so that the young plants on severe competition. Rods ol ircrowded and exposed to very were given to all the plants to to~ or wood of equal diameter each pair reached the summit :: up; and as soon as one of rod was placed on each sid were measured. A single only the tallest plant on eac~ ~fd the crowded pot, No. III., and e was measured. TABLE I (First Ge nera tw. n. ) ~ No. of Pot. Seedlings from I Seedlings from l Crossed Plants. Self-fertilised Plants 1- - Inches. Inches. I. 87 n 69 87 4 89 B. 66 73 - ]J. 88 68~ 87 60~ - III. 77 57 Plants crowded; the tallest one mea-sured on each side. I Total in inches. 516 I 394 I The average height of the . whilst that of the six self-fe:t~i~;~ss~d pla~ts is here 86 inches, so that the crossed plants are to th p a~ts Is .o~Jy 65.66 inches, !00 to 76. It should be observed t:a:~::fe~~~Ised in _height as o a few of the crossed lants b . IS I erence IS not due the self-fer~ilised bein: extrem~~g s~xtremely tall, or to a few of plants a~taming a greater hei htyth ort, b'_lt to all the crossed three pairs in Pot I w g an their antagonists. The tll e d.I fference was so.m eetirme ems ears urt ed at t wo e~rh.e r periods, and g ea er and sometimes less than that |