HARDWICKE'S SCIENCE-GOSSIP. 



24: 



FERTILIZATION OF ORCHIDS WITHOUT POLLEN. 



By J. H. A. HICKS, F.R.H^S. 



• URING the last two 

 years I have made 

 many observations 

 and experiments in 

 reference to "Par- 

 thenogenesis " in 

 flowers of the Or- 

 chidacere. Irritat- 

 ing the stigmatic 

 surfaces of many 

 flowers nearly al- 

 ways resulted in 

 the swelling of 

 ovaries and the 

 production of par- 

 thenogenetic or 

 adventive seeds. 



Treub once dis- 

 covered a larva in 

 the ovary of Lipa- 

 ris latifolia, which 

 apparently seemed to subsist on the juices secreted 

 within the ovarian cavity ; by its movements, and 

 without the interference of pollen, the ovules were 

 apparently stimulated into development. 



Darwin, in the first edition of his great work on the 

 " Fertilization of Orchids," mentioned that the ovaria 

 of matured flowers of Acropera do not contain any 

 ovules, but in the second edition of the same work he 

 says, " I erred greatly in the interpretation of this 

 fact, for I concluded that the sexes were separate. I 

 was, however, soon convinced of my error by Mr. 

 Scott, who succeeded in artificially fertilizing the 

 flowers with their own pollen. A remarkable dis- 

 covery by Hildebrand, namely, that in many orchids 

 the ovules are not developed unless the stigma is 

 penetrated by the pollen-tubes, and that their develop- 

 ment occurs only after an interval of several weeks or 

 No. 335. — November 1892. 



even months, explains the state of the ovarium in 

 Acropera, as observed by me. According also to 

 Fritz Muller, the ovules of many endemic Epiden- 

 drea? and Vandese in Brazil remain in a very imperfect 

 state of development for some months, and even in 

 one case for half a year, after the flowers had been 

 fertilized. He suggests that a plant which produces 

 hundreds of thousands of ovules would waste much 

 power if these were formed and did not happen to be 

 fertilized, and we know that fertilization is a doubt- 

 ful and difficult operation with many orchids. It 

 would therefore be an advantage to such plants, if the 

 ovules were not at all developed until their fertiliza- 

 tion was assured by the pollen-tubes having already 

 penetrated the stigma." 



In many orchid flowers the ovules are dormant 

 and extremely rudimentary, but they can be developed 

 into parthenogenetic or adventive seeds by mechanical 

 irritation of the stigma without pollination. And it 

 does not always follow because suitable pollen has 

 been applied to the stigmatic surface of a flower that 

 all the ovules will develop into good seeds. For in 

 many flowers after pollination the ovary begins to 

 lengthen, and although the pollen-tubes also lengthen, 

 only a few of the ovules are fertilized by them, the 

 others being developed into parthenogenetic seeds 

 through irritation. 



Henslow, in his highly-interesting volume, " The 

 Structure of Flowers," refers to some of Mr. O'Brien's 

 experiments, who says that, "By placing small pieces 

 of grit on the stigma, I found that the ovaries would 

 swell in many cases, just as though the flower had 

 been properly fertilized by pollen. This same result 

 often takes place in orchid flowers under cultivation, 

 and seed-vessels are obtained of full size, but, of 

 course, with no vitality in the grains within." 



Three flowers of Orchis mascula and two of Ophrys 

 apifcra were treated in the same manner, and resulted 



M 



