as a Proof of the two different Effects of the Pollen. 171 



minal corpuscles were distinctly evident, but the cords of the 

 pollen-tubes were unchanged as before. Finally, on the 12th 

 of May, when the diameter of the fruit was 25 niillim., and its 

 length 80 millim., the first two or three cells of the embryo 

 were formed, one of the germinal corpuscles had disappeared, 

 and the pollen-tubes were seen in a decaying state between the 

 ovules. 



Thus we see that a space of four months (January 10 to May 12) 

 was required in order that, after the application of pollen to the 

 stigma of a flower (the ovarium of which contained no ovules), 

 the ovules might attain perfection, and the formation of the 

 embryo begin. 



Having thus described the observations made on Dendrohium 

 nobile, I pass over the experiments on other species, and proceed 

 at once to give the general results of my observations. 



The experiments and observations were made on thirty different 

 species of Orchids, of which nine were tropical and twenty-one 

 indigenous ; therefore we may safely extend the results to the 

 whole Orchidaceous family as follows : — 



1. In the recently expanded flowers of Orchids the ovules 

 are never fully developed. The degrees of development are 

 very different : there are some species (for instance, Listera 

 ovata and Neottia nidus-avis) that have almost perfect ovules, 

 which are incurved and have both of the coats, but the outer 

 is as yet shorter than the inner, and the embryo-sac is not yet 

 to be seen in the nucleus ; in other species (for instance, in 

 Dendrohium nobile) the formation of the ovules has not yet com- 

 menced, even the placentse are not yet fully developed, but ap- 

 pear only as three narrow undulated stripes running down the 

 walls of the cavity of the ovarium, and the bifurcation of every 

 placenta is only slightly indicated. Between these extremes of 

 development there are different degrees of perfection of the 

 ovules. 



2. After the application of the pollen to the stigma, the en- 

 largement of the ovarium begins ; at the same time the ovules 

 become more and more perfect, or if there were only the pla- 

 centse, the ovules begin to appear after a certain time as minute 

 papillse projecting from the surface of the placenta. The en- 

 largement of the ovarium begins before the pollen-tubes reach 

 the placentse or the ovules; in the same manner the ovules 

 begin to grow without being touched by the pollen-tubes. 

 From this it is clearly evident that the tubes of the pollen have 

 no direct influence on the original development of the ovules, 

 but that these tubes first act on the enlargement of the ovarium 

 only, and by this enlargement indirectly on the ovules. Flowers 

 that have no pollen applied to their stigmata do not wither so 



12* 



