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Show 288 CONSTITUTIONAL VIGOUR 0IIAP. VIII. After the germinating seedlings had been planted in pairs on the opposite ::;ides of several pots, the ren1aining seeds, whether or not in a state of germination, were in most cases sown very thickly on the two sides of an additional large pot ; so that the seedlings came up extremely crowded, and were subj ected to extremely severe competition and. unfavourable conclitions. In such cases the crossed plants almost invariably showed a greater superiority over the self-fertilised, than did the plants whieh grew in pairs in tho pots. Sometimes crossed. and self-fertilised seeds were so,vn in separate rows in the open ground, which was kept clear of lvecds ; so that the seedlings wore not su bj ectecl to any competition with other kinds of plants. Those however in each row had to struggle with the adjoining on sin the same row. vVhen fully grown, several of the tallest plants in each row were selected, measur d, and compared. The .result was in several cases (but not so invariably as might have been expected) that the crossed plants did not exceed in height the self-fertilised in nearly so great a degree as when grown in pairs in the pots. '_llh us with the plants of Digitalis, which competed together in pots, the crossed wore to the self-fertilised in height as 100 to 70; whilst those which were grown separately yvere only as 100 to 85. Nearly the smne Tcsult was observed with Brassica. With Nicotiana the crossed \vere to the self-fertilised plants in height, when grown extren1ely crowded together in pots, as 100 to 54; when grown much less crowded. in pots as 100 to 66, and when grown in the open ground, so as to be subjected to but little competition, as 100 to 72. On t~e other hand with Zea, there was a greater difference m heio·ht between the crossed. and self-fertilised plants gro·bw ing on t of doors, than between the pal.l 's wh ' h IC CHAP. VIII. OF THE CROSSED PLANTS. grew in pots in the hothouse; but this may be attributed to the self-fertilised plants being more tender, so that they suffered more than the crossed, when both lots were exposed to a cold and wet summer. Lastly, with one out of two series of Reseda odorata, oTolvn out of doors in rows, as well as with Beta ~ulgaris, the crossed plants did not at all exceed the s.elffertilised in height, or exceeded them by a mere tn:fle. The innate power of the crossed plants to resist unfavourable conditions far better than did the selffertilised plants, was shown on two occasions in u curious manner, namely, with Iberis and in the third gene.ration of Petunia, by the ~reat. ~uperiorit! in height of the crossed over the self-fertihsecl seedhngs, when both sets were grown under extremely unfavourable conditions; whereas owing to special circumstances exactly the reverse occurred with the plants raised from the same seeds and grown in pairs in pots. A nearly analoo-ous case was observed on two other occasions with ;lants of the first generation of Nicotiana_. . . The crossed plants always withst~od the InJUI'lo~s effects of being suddenly removed Into the open au after having been kept in the greenhous~ better than did the self-fertilised. On several occasions they also resisted much better cold and intemperate weather. This was manifestly the case with some crossed and self-fertilised plants of Ipomooa, which were suddenly moved from tho hothouse to the coldest part of a cool greenhouse. The offspring of plants of the eighth self-fertilised generation of Mimulus crossed by a fresh stock survived a frost whieh killed every single selffertilised and intercrossed plant of the same old stock. Nearly the same result follo,vecl with some crossed a_nd self-fertilised plants of Viola tricolor. Even the t1ps of the shoots 9f the crossed plants of Sarothamnus u |