THE POLLEN-TUBE. 409 



wards, and the anthers that surround them retire 

 and shrivel up, after having lost all their pollen ; 

 but at the same time the pollen, which was deposited 

 on the outside of the style, detaches itself, and the 

 hairs that covered the surface disappear." -^ 



Dr. Lindley remarks in relation to these hairs, 

 that if a longitudinal slice of a young style be ex- 

 amined before the pollen is emitted, that it will be 

 seen that these hairs are found formed without any 

 partitions, being an external lengthening of the epi- 

 dermis. These hairs, having become covered with 

 grains of pollen, begin to retract into cavities of 

 about one-half their depth, immediately below them 

 in the cellular tissue. 



Soon after the pollen grains reach the stigma 

 they commence to emit a tube, which, according to 

 Dr. Lindley, does not exceed the one fifteen-hun- 

 dredth or one two-thousandth of an inch in diameter. 

 It reaches down to the placenta and to the foramen, 

 or orifice of the ovule. Among the many methods 

 which are provided for the fertilization of the ovule, 

 when the position of the foramen is peculiar, and 

 which are described by that distinguished author, is 

 that of Euphorbia Lathyris, where " the apex of the 

 nucleus is protruded far beyond the foramen, so as 

 to lie within a kind of hood-like expansion of the 

 placenta ; in all campylotropal ovules, the foramen 

 is bent downwards by the unequal growth of the 



1 As quoted by Dr. Lindley in his " Introduction to Botany." 



35 



