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Show 156 LATHYRUS ODORATUS. CHAP. v. down, in the same manner as bees ought to do; and then pods were generally formed, but from some cause often dropped off afterwards. One of my sons caught an elephant sphinx-moth whilst visiting the flowers of the sweet-pea, but this insect would not depress the wing-petals and keel. On the other hand, I have seen on one occasion hive-bees, and two or three occasions tho MegachJle willughbiella in the act of depressing tho keel; and these bees had the under sides of their bodies thickly covered with pollen, and could not thus f~til to carry po11en frum one flower to the stigma of another. Why then do. not the varieties occasionally intercross, though this would not often happen, as insects so rarely act in an efficient manner? The fact cannot, as it appears, be explained by the flowers being se1f-fertilised at a very early age; for although nectar is sometimes secreted and pollen adheres to the viscid stigma before the flowers are ful ly expanded, yet in five young flowers which were examined by me the pollen-tubes were not exserted. Whatever the cause may be, we may conclude, that in England the varieties never or very rarely intercross. But it does not follow from this, that they would not be crossed by the aid of other and larger insects in their native country, which in botanical works is said to be the south of Europe and the East Indies. Accordingly I wrote to Professor Delpino, in Florence, and he informs me ('that it is the fixed opinion of gardeners there that the varieties do intercross, and that they cannot be preserved pure unless they are sown separately." It follows also from the forPgoing facts that the several varieties 0f the sweet-pea must have propagated themselves in England by self-fertilisation for very many generationR, since the time when each new variety fir~t appeared. From the analogy of the plants of Mimulus and Ipomrna, which had been self-fertilised for several generations) and from trials previously made with the common pea, which is in nearly the same state as the sweetpea, it appeared to me very improbable that a cross between the indLviduals of the same variety would benefit tho offspring. A cross of this kind was therefore not tried, which I now regret. But some flowers of the Painted Lady, castrated at an early age, were fertilised with pollen from the Purple sweet-pea; and it should be remembered that these varieties differ in nothing except in the colour of their flowers. The cross was manifestly effectual (though only two seeds were obtained), as was shown by the two seedlings, when they flowered, closely resembling CHAP. v. LATHYRU ' ODORATUS. their father, the Purple pea, xcopting that they were a little lighter coloured, with their keels slightly streaked with pale purple. SeE:ds from flowe1· . pontaneously self-fortili ed under a ne~ were at the same time saved fron1 the ·amb mother-plant, the Pamted Lady. These seeds unfortunately did not germinate on sand at the eamo time with the crossed so ds, so that they could uot be planted simultaneously. One of the two crossed seed in a state of germination was planted in a pot (No. I.) in whjch a self-fertilised seed in the awe state had been planted four days before, so that this latter seedling had a great advantage over the crossed one. In Pot II. the other cros"ed seed was planted two ~a) s before a self-fertilised one; so that here the croRsed seedlm~ had a considerable advantage over the self-fertilised one. But this c:ossed seedliug had its summit gnawed off by a slug, and. ~vas m consequence for a time quite beaten by the selfftJrtlhsed ~lant. Neverthele s I allowed it to 1·emain and so ~~at was Its constitutional vigour that it ultimately be~t its unInJured self-fertilised rival. When all four plants were almost fully grown they were mea u1·od, a here shown:- TABLE LIV. Lathyrus odoratus. No. of Pot. Cros ed Plants. clf-fertili ed Plants. -- - - lnche . Inches. I. 80 64g II. 78~ 63 - -- Total in inches. 158•5 127•5 Th . fer . ~two cross~d plants here average 79 · 25, and the two self-thet~~ Ised 63 · 75 Inches in height, or as 100 to 80. Six flowers on f two crossed plants were reciprocally crossed :with pollen rom the other plant, and tho six pods thus produced contained to n an average si x: peas, WI' th a maxi. mnm I. n one of seven. Eio·h-ehe~ hspontaneously self-fertilised pods from the Painted Lady w lC I d . ' m ' as a rea Y stated, had no doubt been self-fertihscd for any p.r evious g·e nei·a t w' ns, con t ai·n ed on an average only 3 · 93 opfe as~ W.i th a maxi· mum I· n one of. five peas; so that the number P as In the crossed and self-fertilised pods was as 100 to 65. |