290 AXXUAL OF SCIENTIFIC DISCOVERY. 



these results are true, the vegetable machinery would seem to work 

 at a loss, and with a real, though it be a small, waste of material ! 

 When any carbonic acid taken into the leaves passes off unchanged, 

 so much work is not done ; but there is no waste or loss in the process 

 of manufacture. But, looking at the food of plants and their pro- 

 ducts, comparing the raw material with the manufactured article, 

 it seems apparent that any carbonic acid which is reduced to car- 

 bonic oxide, and given off as such, is so much loss or waste ! We 

 may avoid this unwelcome conclusion by the supposition that the car- 

 bonic oxide and carburet of hydrogen are products of the decompo- 

 sition of some of the vegetable matter coetaneous with vegetable 

 assimilation, but no part of that process itself. This is the more prob- 

 able, since it cannot reasonably be supposed that carbonic acid sup- 

 plied to the foliage is resolved into oxygen and carbonic oxide and 

 both set free, which seems to be the alternative. 



REPRODUCTION OF ORCHIDS. 



Much curious information in relation to the above subject has been 

 brought out by Mr. Darwin, the well-known English naturalist, in a 

 recently-published work. Of these curious plants, it is stated that 

 433 genera, including about 6,000 species, are now known; and, as 

 may be readily imagined, the natural provision for their reproduction 

 is strikingly efficient. Of this, Mr. Darwin testifies from his own 

 observation. He says : 



" I was curious to estimate the number of seeds produced by 

 orchids ; so I took a ripe capsule of Ceplialantliera grandiflora, and 

 arranged the seeds as equably as I could in a narrow hillock, on a 

 long ruled line, and then counted the seeds in a length, accurately 

 measured, of one-tenth of an inch. They were 83 in number, and 

 this would give for the whole capsule 6,020 seeds; and for the four 

 capsules borne by the plant 24,000 seeds. Estimating in the same 

 manner the smaller seeds in Orchis maculata, I found the number 

 nearly the same, viz., 6,200 ; and, as I have often seen above 30 cap- 

 sules on the same plant, the total amount will be 186,300, a pro- 

 digious number for one small plant to bear. As this orchid is peren- 

 nial, and cannot in most places be increasing in number, one seed 

 alone of this large number, once in every few years, produces a ma- 

 ture plant. I examined many seeds of the Cephalanthera, and very 

 few seemed bad. To give an idea what the above figures really 

 mean, I will briefly show the possible rate of increase of O. maculata. 

 An acre of land would hold 174,240 plants, each having a space of 

 six inches square, which is rather closer than they could flourish 

 together; so that, allowing 12,000 bad seeds, an acre would be thickly 

 clothed by the progeny of a single plant. At the same rate of in- 

 crease, the grandchildren would cover a space slightly exceeding the 

 island of Anglesea; and the great-grandchildren of a single plant 

 would nearly (in the proportion of 47 to 50) clothe with one uniform 

 green carpet the entire surface of the land throughout the globe ! " 



Mr. Darwin has also ascertained that self-fertilization is a very rare 



. event with orchids, and that most species, through a curious provision 



of nature, absolutely require the aid of insects for their reproduction. 



