Feb. 2 2, 1877] 



NATURE 



359 



view of a flower, from which all the perianth except the 

 labellum has been removed), a represents the anther con- 

 taining the pollinia, and prolonged above into a long point, 

 an the antennae, which are rigid, curved, hollow horns 

 tapering to a pomt ; but the two differ from one another in 

 this respect, that the apex of the left-hand one bends up- 

 wards, while the right-hand one hangs down, and is 

 apparently almost always paralysed and functionless ; 

 / is the labellum ; d the disc of the poUinium, which is 

 remarkably large and viscid ; pd the pedicel of the pol- 

 linium ; s the stigmatic chamber, which is of course func- 

 tionless in the male flower. The action of the parts is 

 thus described by Mr. Darwin :— When the left-hand 

 antenna is touched, the edges of the upper membrane of 

 the disc, which are continuously united with the surround- 

 ing surface, instantly rupture, and the disc is set free. 

 The highly elastic pedicel then instantly flirts the heavy 

 disc out of the stigmatic chamber with such force that 

 the whole poUinium is ejected, bringing away with it the 

 two balls of pollen, and tearing the loosely- attached 

 spike-like anther from the top of the column. The pol- 

 linium is always ejected with its viscid disc foremost, and 

 with such force that it is thrown to a distance of two or 



Fjg. 4. —Mormodes igneei. Lateral view of flower with one of the sepals 

 and one of the petals removed, a. anther ; pd, pedicel of poUinium ; 

 s, stigma ; /, labellum , Is, lateral sepal. 



three feet. On one occasion Mr. Darwin touched the 

 antenna of an allied species, C callosum, while holding 

 the flower at about a yard's distance from the window, 

 when the poUinium hit the glass, and stuck by its adhe- 

 sive disc to the smooth vertical surface. A series of ex- 

 periments showed that even violent concussion of any 

 other part of the flower except the antenna produced no 

 effect whatever in disturbing the pollinia. 



4. Mormodes i^nea. — The genus Mormodes belongs 

 also to the small family Catasetidse ; the pollinia are 

 again violently ejected, as in Catasctum j but the mode 

 in which this is effected is somewhat different, and very 

 curious. The appearance presented by the flower is re- 

 presented in Fig. 4. The base of the column is bent 

 backwards, at right angles to the ovary, then resumes 

 an upright position, and is finally again bent near the 

 summit. It is also twisted so that the anther, rostellum, 

 and the upper part of the stigma face one side of the 

 flower, to the right or left, according to the position of the 

 flower in the spike. In the drawing, a represents the 



anther, which is elongated and triangular, but does not 

 extend to the apex of the column. A group of spiral 

 vessels runs up the column as far as the summit of the 

 anther ; they are then reflexed, and run some way down 

 the anther- case. The point of reflexion forms a short thin 

 hinge, by which the top of the anther-case is articulated to 

 the column beneath its bent surface ; and this hinge 

 appears to be the sensitive portion of the structure, con- 

 veying any stimulus from a touch to the disc of the 

 pollinia, and causing the eje:tion of the litter, pd is the 

 pedicel of the polliniurn, covering the rostellum ; j-/, the 

 stigmatic surface, whicl^ extends down to the base of the 

 column, and is hollowed out into a deep cavity at its 

 upper end ; / is the very remarkable labellum, narrowed 

 at the base into a nearly cylindrical foot-stalk, and its 

 sides so much reflexed as almost to meet at the back, 

 forming a folded crest at the summit of the flower. Near 

 the summit it has a slight cavity, into which the summit 

 of the column fits, fixing it in its place. The whole 

 labellum ip compared by Mr. Darwin to a cocked hat 

 supported by a foot-stalk, and placed on the head of the 

 column. Is are the two lower sepals, which hang down 

 like wings ; the upper sepal and one of the lateral petals 

 have been cut off. By a number of experiments Mr. 

 Darwin found that the minute hinge in the anther-case 

 already described is the only portion of the flower that is 

 sensitive to touch. When an insect lights on the folded 

 crest of the labellum, the only convenient landing-place, 

 he will lean over the front of the column in order to gnaw 

 or suck the bases of the petals, which are filled with a 

 sweet fluid. In so doing, he will disturb the summit of 

 the column which fits into the cavity of the labellum ; this 

 will press on the hinge in the anthsf-case ; the stimulus 

 will then be conveyed to the poUinium-disc, and the 

 poUinium will be violently ejected. Owing to the 

 peculiar structure of the parts, guided by the hinge, 

 which now serves a second function, the direction in 

 which the poUinium flies is necessarily vertically upwards. 

 If no object is in the way, it is projected perpendicularly 

 up in the air, an inch or two above and close in front of 

 the terminal part of the labellum, and would then alight 

 on the folded crest of the labeUum immediately above 

 the column. But if the insect which has caused the dis- 

 turbance remains in the same position, the poUinium will 

 necessarily alight on his head, and will thus be carried 

 off to fertilise another flower. The poUinium has, how- 

 ever, still the anther-cap attached to it ; this drops off, as 

 the pedicel dries on exposure to the air and graduaUy 

 straightens itself from the almost hoop-shaped form 

 which it bore when ejected ; and when this has been 

 done, the pollen-masses attached to the head of the in- 

 sect are precisely in a position to strike against the stig- 

 matic surface of the next flower visited, 



Other instances, almost as extraordinary, could be cited 

 of the special contrivances met with iii species belonging 

 to this order, to insure cross-fertilisation rather than self- 

 fertUisation of the flowers. A. W. B. 



THE MOVEMENT OF THE SOIL-CAP 



A MID all their general tameness the Falkland Islands 

 -'^ boast one natural phenomenon which is certainly 

 exceptional, and at the same time very effective. 



In the East Island most of the valleys are occupied by 

 pale-grey glistening masses, from a few hundred yards to 

 a mile or so in width, which look at a distance much like 

 glaciers descending apparently from the adjacent ridges, 

 and gradually increasing in volume, fed by tributary 

 streams, until they reach the sea. Examined a little more 

 closely, these are found to be vast accumulations of blocks 

 of quartzite, irregular in form, but having a tendency to 

 a rude diamond shape, from two to eight or ten or twenty 

 feet long, and perhaps half as much in width, and of a 

 thickness corresponding with that of the quartzite bands 



