5° 



HA RD WICKE'S SCIENCE- G OS SIP. 



tact with them only by the agency of insects. This 

 is also the case with Sophronitis grandiflora, Lalia 

 cinnabflrina, Chysis aurea, Phajiis grandifolius, and 

 Pliajus IVallissii. 



In Oncidhtm graitde, Brassia metadata, and. So- 

 bralia macrantha, the caudicles to which the pollen- 

 masses are attached lie within a cleft between the 

 masses, more or less invisible, and attached at the 

 lower ends to a curved pedicel, which is connected 

 with the gland, varying in shape and size, and viscid 

 on its inferior surface. 



The pedicel, in many orchid flowers, is highly 

 elastic and exceedingly sensitive ; and the sensibility 

 of the pedicel causes the pollinia to undergo the 

 curious movement of depression, which is essential to 

 secure fertilization. 



When a suitable insect alights on the lip or labellum 

 of the flower, it at once proceeds to insert its head 

 into the stigmatic chamber, in order to obtain the 

 nectar contained in the nectary with its proboscis ; 

 in so doing the head strikes against the rostellum, 

 with just sufficient force to rupture its outer mem- 

 brane in a transverse line ; when this is effected, the 

 anterior part of the rostellum is easily depressed, and 

 the viscid gland, or disc, becoming exposed, cannot 

 fail to touch and adhere to the head of the insect ; so, 

 when the insect withdraws, the pollinia, or pollinium, 

 is also withdrawn, and the viscid matter of the gland 

 soon becoming dry, firmly adheres to the head of the 

 insect. Then the pedicel to which the caudicle is 

 attached contracts, and causes the pollinium to be- 

 come depressed, by which movement the pollen- 

 packets are then so adjusted as to effectually strike 

 the stigma when the insect next visits a similar flower, 

 The movement of depression is completed in 

 Odontoglossum triutnphans and Odontoglossum vexil- 

 lariuni cobbianum, in twenty seconds ; in Brassia 

 maculata, Vanda teres, Stanhopea tigrina, Maxillaria 

 grandiflora, sErides odoratum, Oncidhim grande, and 

 Saccolahium blumei majus, in about thirty seconds, 

 while in Rodriguezia snaveolens, the movement is 

 completed in about four hours. 



The pollinium in Acrop>era loddigesii, after removal 

 from the anther, undergoes the movement of depres- 

 sion ; but in this case, Darwin considers the move- 

 ment superfluous, "for the stigmatic cavity lies high 

 up at the base of the rectangularly-projecting rostel- 

 lum." The viscid matter of the disc in Sarcanthus 

 teritifolius, Odontoglossum triumpkans, and Odonto- 

 glossum Oerstedii, sets hard after removal, in about 

 two minutes ; while in Lyca.de Skinnerii, and Chysis 

 aurea, it takes thirty minutes to become perfectly dry. 



Dr. Darwin, in his highly-interesting and valuable 

 work on " orchids " (many of whose experiments and 

 observations on orchid flower s I can fully confirm, 

 having spent much time in making similar experiments 

 and observations), says : "The discs and pedicels of 

 the pollinia present great diversities in shape, and an 

 apparently exhaustless number of adaptations. Even 



in species of the same genus, as in Oncidium, these 

 parts differ greatly." Probably, the great diversity 

 in shape and size, exhibited by the discs and pedicels,, 

 may be partially co-related to the certain parts of 

 those insects which visit the flowers in a state of 

 nature. 



In flowers of Catasetum saccatum, the discs are 

 very large and viscid. An insect visiting one of these 

 flowers does not approach the discs, but, alighting on 

 the conspicuous and convenient labellum, must un- 

 avoidably touch one of the two highly-irritable curved 

 antenna-like prolongations. This movement instantly 

 ruptures the delicate membrane, retaining the pedicel 

 in a state of tension, and effects the expulsion of the 

 pollinia, which curious enough is sure to strike and 

 adhere to the head of the intruder ; the insect being 

 startled by the blow, at once flies off. Should this 

 insect visit a female plant, the pollinia, now adjusted 

 to a proper position through the elasticity of the 

 pedicel, cannot fail to come in contact with the 

 viscid stigma, and consequently fertilization takes 

 place. 



In Calanthe dominii the disc is oval and viscid, 

 but is destitute of a pedicel. To this disc eight 

 radiating club-like masses of pollen are attached by 

 extremely short caudicles. The pollinia do not 

 undergo the usual movement of depression. For an 

 insect having visited one flower and secured the disc, 

 would, on entering the nectary of another flower, 

 bring the appended pollinia in contact with the lower 

 part of the rostellum, thus causing the pollinia to 

 curve down and strike the viscid stigma. Occasion- 

 ally some of the central pollen masses are inserted 

 through the opening in the rostellum, and adhere to 

 the viscid rim of stigmatic tissue. 



In sErides odoratum, we have an example of the 

 great elasticity of the pedicel. It is secured at its 

 lower extremity by the disc, and at its upper extremity 

 by the anther. If the disc is removed by some intrud- 

 ing object, the pedicel immediately springs up, thus 

 liberating the pollinium from the anther-case. When 

 this is completed, another movement takes place, by 

 which the pedicel is restored again to the original 

 position it held in relation to the disc while attached 

 to the rostellum. This second movement is hygro- 

 metric, for when the pollinium, after removal, is 

 placed in water, it moves back to precisely the same 

 position it previously held, consequent on the elasticity 

 of the pedicel ; but, when removed from the water,, 

 the act of depression again takes place. 



The flowers of Oncidium ornithorhyncum, afford! 

 another curious example of the hygrometric movement 

 of the pedicel. Should an insect visiting one of the 

 flowers remove the elongated pedicel from the ros- 

 tellum, the pedicel becomes shorter, by moving back- 

 wards upon itself. The stigma being shallow, this 

 movement is of utmost importance to the flower 

 for were the pedicel to remain the same length after 

 removal, the pollinium could not effectually come in, 



