as a Proof of the two different Effects of the Pollen. 173 



Time from the Application of Pollen Degree of Development of the Ovules 

 to the Stigma to the incipient in the expanded Flower, 



formation of the Embryo. • 



Cephalanthera grandiflora, end of Papillse a little incurved; begin- 



May to beginning of July ; 5-6 ning of ii very small. 



weeks. 

 Eria stellata, Feb. 13 to April 15 ; Placentae irregularly fringed, with 



2 months. very small wartlike projections. 



Bletia Tankervillics, Jan. 26 to end The same. 



of March ; more than 2 months. 

 Dendrobium nobile, Jan. 10 to May Placentae undulated, not fringed. 



12; 4 months. 

 Cymbidium sinense, Dec. 9 to be- The same. 



ginning of June (?) ; 6 months (?). 



It appears that those ovules which vi^ere most developed in 

 the expanded flower (for instance, in Listera ovata and Neottia 

 nidus-avis) wanted only nine days to attain perfection and to be 

 impregnated by the pollen-tubes ; while, on the other hand, in 

 those cases where even the placentae were not as yet developed 

 {i. e. in Dendrobium nobile) an interval of four (in one case per- 

 haps of six) months elapsed before the embryo began to be 

 formed. Respecting the differences of temperature in the dif- 

 ferent years, it will scarcely be necessary to add that the above- 

 mentioned intervals of time will not be quite the same every 

 year. 



Soon after the commencement of the formation of the embryo, 

 the six cords of the pollen-tubes disappear. E.. Brown says (/. c. 

 p. 707) that they are to be met with even in the ripe capsule ; 

 but I could not find them anywhere. I saw them very often 

 in a decaying state, some time after the impregnation of the 

 ovules. 



4. From these observations it follows that, in the formation of 

 the fruit in Orchids, the pollen acts in two different ways : on 

 the one hand, it effects the enlargement of the ovarium and the 

 development of the imperfect ovules without the pollen-tubes 

 directly touching the ovules ; on the other hand, it impregnates 

 the ovules, directly touching the embryo-sac, and determining 

 the development of one germinal corpuscle into an embryo. It 

 is not necessary to allude further to the observations on this last 

 point, as they only confirm known facts. 



Having given the results of a long series of observations and 

 experiments made on Orchidaceous plants, I may be allowed to 

 add a few words on the impregnating action of pollen in general. 

 It is a question, often spoken of among botanists, whether the 

 pollen acts only in impregnating the ovules, or whether, inde- 

 pendent of this power, it has yet another, and what this other 

 power might be, and in which way it might act. Professor 



