PROGRESS OF VEGETABLE PHYSIOLOGY. 411 



tinuous spiral tubes separate in the course of development more or less 

 completely by constriction, and form articulations arranged in series. 



" The cross partitions of the single articulations of the metamorphosed 

 spiral tubes are either broken through by a very large aperture or by a 

 number of fissures and longitudinal pores : nay, even the oblique partitions 

 of the large dotted tubes in the wood of some species of Ephedra are 

 pierced, and that by the large round holes, wrhich generally occur in them 

 arranged in two parallel rows. M. Mohl observes that phytotomists have 

 considered these horizontal sides as lateral sides of the tubes, which was 

 also probably owing to bad instruments, for the inclination of these hori- 

 zontal walls to the lateral is so exceedingly small, that they may even be 

 regarded as inclined terminal surfaces of the prosenchymatous cells, with 

 which the superposed cells stand in connexion ; I at least have declared 

 in favour of this latter opinion. The disappearance of the horizontal walls 

 in the dotted spiral tubes is, as M. Mohl thinks, to be compared to the 

 formation of the vessels of the latex, which also are said to originate from 

 cells standing above one another, as M. Unger (see p. 30) has tried to 

 render probable by a drawing. The most varied views exist however on 

 this subject, and are as diametrically opposed to one another as those on 

 the metamorphosis of the spiral tubes. According to M. Schultz, con- 

 strictions and the formation of articulations of the proper vessels originate 

 with the advancing age of the plant ; in the young state these vessels were 

 still unarticulated. According to my observations, the proper vessels are 

 neither in their youth nor old age provided with cross partitions, but ex- 

 hibit in the latter state some constrictions which are independent of exter- 

 nal circumstances. According to M. Mohl, the continuous vessels of the la- 

 tex originate from cells, whose cross partitions disappear ; to which, in con- 

 sequence of numerous researches on this subject, I am decidedly opposed. 



" The distinction between dotted and reticulated spiral tubes consists, 

 according to M. Mohl, in this : — that in the latter the organic matter used 

 for the further development of the vessels does not deposit itself in the form 

 of a membrane between the coils of the spiral fibre, but goes to increase 

 the spiral fibre itself, both with respect to its thickness as well as to its 

 breadth. In the dotted (porous) spiral ducts of dicotyledons, on the con- 

 trary, this substance is deposited in the form of a membrane between the 

 coils of the spiral fibre on the original membrane of the vessel. 



" Neither can I concur in these statements : the thickening of the walls of 

 both those stages of metamorphosis of the spiral tubes takes place in quite 

 a similar manner ; the principal reason for the change into reticulated and 

 into dotted spiral tubes is to be found only in the arrangement of the indi- 

 vidual coils of the spiral fibre. If the coils are widely apart, they may fall 

 merely into annular tubes, or be metamorphosed into reticulated spiral 

 tubes ; on the contrary, if the coils are close together, only striped and 

 dotted spiral tubes, and not reticulated, can originate. This is very easily 

 confirmed in stems of Cacti, in the inflorescence of Musa, &c." 



The beautiful observations of Schwann^ on the presence of 

 a fungus, Saccharomyces, in fluids undergoing the vinous 

 fermentation, are too important to be passed over without 

 notice, even in a brief review : — 



" He saw in the beer-yeast most globules cohering in series ; they were 

 partly round, but for the most part oval granules of a yellowish-white 

 colour (they are perfectly colourless in achromatic instruments. — Rep.), 

 which partly occur singly, but generally in series of 2 — 8 or more. Usu- 

 ally one or more distinct series branch off" obliquely on such a series. In 

 short, the whole is an articulated and ramified plant. M. Schwann ob- 



