8 Prof. Chas. Morren on the Cultivation of Vanilla. 



forth numerous aerial roots without giving it the quality of a 

 parasite. In fact, Vanilla is not in the least a parasitical 

 plant. 



The culture consists in twining the branches, cutting, and 

 burning them at their extremity with a hot iron : everything 

 that contributes to stop the sap serves to bring it into flow er- 

 ing state. If a plant blossoms and its flowers are not fecun- 

 dated, it bears new flowers in the following year ; but if it 

 has produced fruit, some years of rest are necessary before it 

 flowers again. The time of its flowering is from February to 

 April, and when it bears fruit they need exactly a year and a 

 day to ripen : this fact has constantly been confirmed at 

 Liege. As the fruit ripens, it falls, and maturation takes 

 place without the aid of the plant. 



§ V. On the Structure of the Flowers of the Vanilla Plant, 



The flower of Vanilla has this peculiarity — that the retina- 

 culum is highly developed, so that this organ forms a curtain 

 suspended before and above the stigmatic surface, thus sepa- 

 rating it completely from the anther, which in its turn in- 

 closes in two cavities, naturally shut, the pulverulent masses 

 of pollen. From this structure it results, that all approxima- 

 tion of the sexes in this orchideous plant is naturally impos- 

 sible. It is thus necessary either to raise the velamen or to 

 cut it when the plant is to be fecundated, and to place in 

 direct contact the pollen and the stigmatic surface. The fe- 

 cundation never fails, and we may be convinced of its success 

 by observing the flower some hours after the operation. If 

 impregnation has been eflected, the petals and sepals reverse 

 inwardly, and the flower droops instead of remaining erect. 

 So soon as the following day the ovarium elongates. 



I followed the development of the pollen tube through the 

 columnar tube and at the septa only to the ovules ; but w hat 

 is remarkable is, that it requires three weeks before the pollen 

 tube seizes the nucleus of the ovule. The formation of this 

 latter part is easily studied in this species, and I have veri- 

 fied on this plant the profound researches of Robert Brown, 

 which are of the greatest accuracy. 



The direct results of this memoir therefore go to prove that 



