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28. — The Feetilisation of Plants. 



By the Rev. George Henslow, M.A., F.L.S., F.G.S., 



Lecturer on Botany at St. Bartholomew's Hospital. 



[A Lecture delivered 8tli March, 1877.] 



I PURPOSE giving you this evening a short account of a new work 

 by Mr. Darwin. As you are all doubtless aware, whatever he 

 undertakes he does thoroughly, and his book on " The Cross- and 

 Self -Fertilisation of Plants," which came out last January, contains 

 observations upon experiments he has been making for several 

 years past. It is a book that takes, I had almost said months, 

 certainly weeks, to digest thoroughly ; and although no one can 

 gainsay the majority of his conclusions, there is one point from 

 which, I think, he has drawn a wrong inference ; and I shall 

 comment upon it. I mean " Self -Fertilisation." My first idea 

 was to make that the subject of this lecture, but I shall take 

 the whole question, and then put before you wherein I think lies 

 his mistake, and I shall be very glad if any one will criticise my 

 views. 



It is just two hundred years ago since Sir Thomas Millington 

 detected the use of the pollen for the fertilisation of the stigma. 

 As soon as that necessity was recognised, the idea very soon followed 

 that flowers were adapted to secure their own seeds by the pollen 

 falling on the stigma of the same flower. I think it was Linnaeus 

 to whom is attributed the statement that both pendulous and erect 

 flowers have the stigmas behiv the anthers, so that the pollen may 

 fall from the latter upon them. Further observations would have 

 shown that this is not universally true. Take, for instance, the 

 common crocus. In the pui-ple variety the stigma is erect and 

 forms a brush, but the stamens are below it. The tops of the 

 anthers only reach a height below the point where the stigmas 

 branch, so that this is a case in which the rule fails. It was soon 

 found that in many instances it would not apply, and it was also 

 noticed that all flowers had not both stamens and pistils in the same 

 flower, e.g. cucumbers and melons ; and similarly with regard to 

 several trees, such as the willow ; so that it was clear there must 

 be some other law than that the pollen should fall on the stigma of 

 the same flower. Hence "intercrossing" was suspected, and 

 Sprengel, a German, in 1790, wrote a very interesting book, in 

 which he noticed a great many plants, the pollen of which it is 

 necessary for insects to carry from one flower to another. "We 

 have, however, to thank Mr. Darwin for elucidating the fact, and 

 establishing, on a thoroughly scientific basis, the necessity for 

 insects to visit conspicuous flowers and carry the pollen from one to 

 another. He was the first English botanist who established that 

 fact, although he has had a great number of followers since ; and 

 anybody who searches regularly into flowers is pretty sure to find 

 some new contrivance. I will mention one of a few recorded by 



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