Natural History. 417 



hood, irrigated from the river of Pasamayo, (called also the river of 

 Chancay,) but Ruiz and Pavon say, they found the plant in the hills, 

 where, as I have before observed, there is no cultivation. As nothing, 

 however, is stated of the nature of the hills, nor of the height at 

 which the plant occurs above the valley, there is still room to 

 suspect that it may have been accidentally introduced, and, indeed, 

 the Indians formerly brought water upon the land from a considerable 

 distance, at a much greater elevation than any that is irrigated at 

 the present day. 



Upon the whole, it may be safely concluded that this important 

 vegetable is really indigenous to Chili ; but with respect to Peru, 

 some further evidence appears necessary to remove all doubt on the 

 subject. The question can only be decided by ascertaining the exact 

 situations in which the plants present themselves at Lima and 

 Chancay, especially with respect to land that is or has been cultivated. 

 It would be interesting, too, to know the colour of the flowers. 



8. NEW FORMS OF CELLULAR TISSUE. 



Dr. J. E. Purkinje has ascertained that the tissue which constitutes 

 the lining of the case of an anther is of a peculiar kind. It consists 

 generally of vesicular cellular tissue, the membranous walls of which 

 are marked with spiral fibres, coiled up in the inside from the one end 

 to the other ; sometimes the fibres are placed like a number of ribs 

 passing from the base to the apex, without any trace of a spiral 

 direction. Occasionally the membrane of the tissue disappears and 

 fibres only remain ; and in some cases the whole of the tissue is 

 reduced to a number of points sticking up from the inside of the 

 anther. It is probable that these and similar observations will throw 

 much light upon the analogy that exists between cellular and vascular 

 tissue. 



9. FUNCTIONS OF SPIRAL VESSELS. 



From the researches of Dr. L. W. T. Bischoff of onn it appears 

 that the spiral vessels of plants contain no fluid, but serve exclusively 

 to convey air, and that this air has from 7 to 8 per cent, more 

 oxygen than the atmosphere. He found by very delicate and re- 

 peated experiments, that the air from the spiral vessels of malva 

 arboreq, contained 27.9 per cent, of oxygen, and cucurbita pepo, at 

 two different times, 29.8 and 27.9 per cent. From the researches of 

 the same author, it seems that the spiral vessel is a delicate pellucid 

 membranous tube, within which a spiral fibre is generated; that 

 when the whole surface of the tube is filled up by the coils of the 

 spiral fibre, a true spiral vessel is the result, and that spurious spiral 

 vessels, or ducts, with all their modifications, are formed by disloca- 

 tions or separations of the spires within the membrane. Dotted 

 ducts, for instance, are, according to Dr. Bischoff, caused by the 

 separation of the spiral fibre into minute points. 



