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Show 230 CANNA WARSCEWICZI. CnAP. VI. selected and measured. The eight tallest crossed plants averaged 30 · 92, and the eight tallest self-fertilised 30 · 7 inches in height, or as 100 to 99; so that they were practically equal. But we should bear in mind that the trial was not quite fair, as the self-fertilised plants had a great advantage over the crossed in being much less crowded in their own row, owing to the large number of seeds which had perished under ground after sprouting. Nor were the lots in the two rows subjected to any mutual competition. XXIX. CANN ACE.JE.-CANNA w ARSCEWICZI. In most or all tho species belonging to this genus, the pollen is shed before the flower expands, and adheres in a masF; to the foliaceous pistil close beneath the stigmatic surface. As the edge of this mass genentlly touches the edge of the stigma, and as it was ascertained by trials purposely made that a very few pollen-grains suffice for fertilisation, the present species and probably all the others of the genus are highly self-fertile. Exceptions occasionally occur in which, from the stamen being slightly shorter than usual, the pollen is deposited a little beneath the stigmatic surface, and such flowers drop off unimpregnated unless they are artificially fertilised. Sometimes, though rarely, the stamen is a little longer than usual, and then the whole stigmatic surface gets thickly covered with pollen. As some pollen is generally deposited in contact with the edge of the stigma, certain authors have concluded that the flowers are invariably self-fertilised. This is an extraordinary conclusion, for it implies that a great amount of pollen is produced for no purpose. On this view, also, the largo size of the stigmatic surface is an unintelligible feature in tho structure of the flower, as well as the relative position of all the parts, which is such that when insects visit the flowers to suck the copious nectar, they cannot fail to carry pollen from one flower to another.* * Del pi no has described (' Bot. Zeitung,' 1867, p. 277, n.nd' Scientific Opinion,' 1870, p. 13fl) tho structure of the flow ' l'S in this genus, but lte was mi taken in thinking that self-fertilisation is impossible, at least in the case of the present species. Dr. Dickio and Prof. Faivre state thut the flowers are f rtilised in the bud, and that ~elf-fertilisation is inevitable. I presume that they were J?isled by the pollen being dcpos1~e~ at a verv et1l'ly period on the pi:Jtll: see , Journal of Linn. Soc. Bot.' vol. x. P· 55, ~nd 'Variabilite des Espcee~,' 1868, p. 158. CHAP. VI. CANNA W ARSCEWIOZI. 231 According to Delpino, bees eagerly visit the flowers in North Italy, hut I have never seen any insect visiting the flowers of the present species in my hothouse, although many plants grow there during several years. N evertbeless these plants produced plenty of seed, as they likewise did when covered by a net; they are therefore fully capable of self-fertilisation, and have probably been self-fertilised in this conntry for many generations. As they are cultivated in pots, and are not exposed to competition with surrounding plants, they have also been subjected for a considerable time to somewhat uniform conditions. This, therefore, is a case exactly parallel with that of the common pea, in which wo have no right to expect much or any good from intercrossing plants thus descended and thus treated; and no good did follow, excepting that the cross-fertilised flowers yielded rather more seeds than the self-fertilised. This species was one of the eaTlier ones on which I experimented, and as I had not then raised any self-fertilised plants for several successive generations under uniform conditions, I did not know or even suspect that such treatment would interfere with the advantages to be gained from a cross. I was therefore much surprised at the crossed plants not growing more vigorously than Lhe selffertilised, and a large number of plants were raised, notwithstanding that the present species is an extremely troublesome one to experiment on. The seeds, even those which have been long soaked in water, will not germinate well on bare sand ; and those that were sown in pots (which plan I was forced to follow) germinated at very unequal intervals of time; so that it was difficult to get pairs of the same exact age, and many seedlings had to be pulled up and thrown away. My experiments were continued during three successive generations; and in each generation the self-fertilised plants were again self-fertilised, their early progenitors in this country having probably been selffertilised for many previous generations. In each generation, also, the crossed plants were fertilised with pollen from another crossed plant. Of the :flowers which were crossed in the three generations, taken together, a Tather larger propoTtion yielded capsules than did those which were self-fertilised. The seeds were counted in forty-seven capsules from the crossed flowers, and they contained on an average 9 · 95 seeds; whereas forty-eight capsules from the self-fertilised :flowers containecl on an average 8 ·45 seeds; or as 100 to 85. The seeds from the crossed flowers were |
