82 GENERAL REVIEW OF THE ORCHIDE.E. 



disceniible difference was observed in the result. The unfertilised 

 flowers of Deii'lroMum nohile continue in perfection from twenty to 

 thirty days according to external circumstances ; the perianth of the 

 fertilised flowers began to fade in two days after pollination ; 

 the up})er part of the column began to thicken and gradually to 

 become hemispherical in shape. Before the expiration of twenty days 

 numerous pollen tubes began to descend into the ovary and to take 

 a position alongside the placentas in six strong bundles, one on each 

 side of the three placentas; the ovary itself thickened and lengthened 

 from day to day with a corresponding development of the placentas. 

 After the twentieth day each placenta divided into two ridges, each 

 of Avhich had produced numerous outgrowths in the form of minute 

 papillae, but as yet without a trace of a true ovule. At the end of 

 two months, however, the placentas were covered with numerous ovules 

 in different stages of development, the pollen tubes still lying fresli 

 on each side of the placentas ; the capsule had attained nearly its full 

 size, but was still succulent and green. In from four to five weeks 

 more the ovules were fully developed, and quite filled up the cavity 

 of the ovary; the embryo-sac and its nucleus were distinctly discernible. 

 Another ovary examined on April 22nd showed that although the ovules 

 had considerably lengthened and the embryo-sac and its nucleus Avere 

 enlarged, no pollen-tubes had yet made their way through the micropyles 

 of the ovules. By the 12th of iMay the formation of the embryo had 

 began, the ovules had reached tlie size of the ripe seed and many of 

 them had divided into two and three cells ; only a few decomposed 

 remains of the pollen-tubes were found. This proved that the period 

 between pollination of the Hower and the fertilisation of the ovary of 

 Dendrohium nohile is about four months. In another fortnight nearly 

 all the ovules were furnished with embryos, and the capsules subse- 

 quently ripened. 



Similar investigations carried on simultaneously with those made of the 

 fructification of Dendrohmm nohile showed that in Pliaius grandlfolius 

 the period from i)ollination to the fertilisation of the oviile is about 

 two months, and in Gypripediam ini<iijne about four months.* And in 

 the case of some of the hardy terrestrial orchids the remarkable fact 

 was elicited that their fructification is effected in a very much shorter 

 time ; thus, the period from pollination to the fertilisation of the ovules 

 of Llstera ovata (Tway-blade ), Neottla Nidus-avis, and Orchis 2iy^'(>i'f^^idalis 

 is only eight or nine days, and of Gymnadenia conopsea, Orchis Mario 

 and 0. mwulaid about a fortnight. The great difference in the periods 

 of fertilisation lictween our native specnes and the epiphytal orchids is 

 ascribed by Dr. Hildebrandt chiefly to climatic ca\ises. 

 Dr. Hildebrandt's investigations were directed chiefly towards the 



* Tlie capsule of Cyimpedium insiync is uot ripe till several mouths at't'nwards. 



