951 



parallel with this latter to the end of the style, where it passes from 

 the cellular tissue of the stigma into the conducting fibres of the ca- 

 nal of the style. When the tube does not enter the cellular tissue of 

 the stigma by the shortest course, but runs to a greater extent free on 

 its surface, the penetration of the tube does not take place at all in 

 most cases, as is seen in Clarkia pulchella. The author now consi- 

 ders the penetration of the pollen-tubes into the canal of the style, 

 where they follow the conducting fibres. The conducting fibres of 

 the canal of the style correspond, as the author says, in their struc- 

 ture to the absorbent hairs (Saughaaren) of the stigma ; in most cases 

 the absorbent hair is nothing more than the most external cell of a 

 series of conducting fibres, which latter is, however, destitute of cu- 

 ticle. The conducting fibies consist always of two membranes lying 

 one within the other, of a mucous membrane and a tubular membrane. 

 The pollen-tubes, however, often perforate the outer membrane, in 

 parts where an open canal occurs, and reach the interior. Although 

 we can trace the tubes as far as the ovary, but no further, a transmis- 

 sion of the fertilizing matter from the tubes adjoining the placenta, 

 into its cellular tissue, takes place ; and it is forwarded to the ovule 

 through the cells or fibres of the funiculus. The author attempts to 

 prove thereby that in plants with many-seeded ovaries, the number 

 of ova presents often a great disproportion to the number of tubes. 

 In CEnothera longiflora, for example, the ovary contained about 

 1000 ova, of which some 250-300 attained complete development. 

 The usual area of a transverse section of 300 tubes is '00785 of a 

 square line ; but the canal of the style close above the ovary has 

 only an area of '00785 of a square line, so that even if it contained 

 nothing but tubes, it would comprise only one-fifth of those which 

 are necessary to fructification ; but in the lower part of the canal of 

 the style of this plant not so many as 50 tubes can be counted at the 

 most. The pollen-tubes also appear of greater duration when they 

 enter the ovum ; but here, namely, in GEnothera longiflora, the au- 

 thor has never found a tube in a single ovum. Since the tube is 

 usually of such a size that it could not easily be contained in the 

 pollen-granule from which it arises, the author considers it probable 

 that the fertilizing material of the granules which have not advanced 

 to the formation of tubes, being absorbed from the surface of the 

 stigma and introduced into the cellular tissue, is taken up by the 

 tubes, and conveyed in common with their proper contents to the 

 spot where impregnation is effected. 



" In the second chapter, epigynous impregnation is treated of, un- 



