EXTRACTS AND ABSTRACTS FROM FOREIGN JOURNALS. 211 



considered the punctum scdiens or macula germinativa of the radicle, and 

 which, in consequence of its being the precise point at which all the or- 

 ganization commences, is continually in process of development. 



The root of Saccharum offidnarum teaches the following facts : 



The cells of the punctum veyetationis, examined under a high power, 

 are the smallest of the root. Their walls are extremely thin and delicate, 

 so much so, that no doubling can be seen between adjacent cells. They 

 contain a homogeneous, non-granular mucilage, which differs but little 

 from the wall of the cell, and represent in some measure the latter in 

 an amorphous state. The cavities of the cells are not equal in all, which 

 would seem to indicate, that in the larger cells partitions are formed which 

 divide the space into two or more compartments. No traces as yet of 

 nuclei can be observed, which appear in cells a little removed from this 

 situation. From this it results, that this point, made up of elementary 

 parts very small and perfectly homogeneous, is evidently organized, 

 and that it differs from parts more fully developed, and into which it is 

 continually being transformed, only by the tenuity of the walls of the 

 cells, and by their homogeneous mucilaginous contents. 



Having thus traced the commencement of the larger vessels, it re- 

 mains to pursue their development in the ascending scale, and the mode 

 in which the vascular utricules, by their apposition, constitute a perfect 

 canal. About 77 millim. from the extremity of the radicle, the vascular 

 utricules are as wide as they are long ; their walls are of extreme tenu- 

 ity, and they contain a mucoid matter, beginning to become granular. 

 At the height of about a line, the cells are five or six times longer, but 

 have not increased in width. They still contain a mucilaginous mass, 

 in which, however, traces of organization can be recognized. It be- 

 gins to coagulate into vesicles, which, when magnified, represent a vas- 

 cular or cellular net- work. At the height of 12 centim., the length of 

 the cells is again doubled, while their width remains the same. The 

 membrane composing them also shows the same homogeneous confor- 

 mation ; but there are now observable, added to its contents, some 

 cellular nuclei. It is not till they have reached the distance of four 

 inches from the extremity of the radicle, that the walls of the vessels 

 appear of any thickness, and at the same time become furnished with 

 rudiments of pores. The smaller vessels, however, become more fully 

 developed, even at the distance of two lines from the extremity. It is 

 a remarkable fact, that those vessels which soon assume the reticulated 

 form, present at first, in the form of their secondary layers, only a spi- 

 ral disposition of the molecules composing them, in which respect they 

 closely represent the type of simple spiral vessels. The metamor- 

 phosis in this case is easily explained, by supposing a partial engorge- 

 ment of the spaces left vacant between the spiral fibres. 



At five inches from the extremity, there is at last evident an organi- 

 zation in the membrane of the large vessels ; nevertheless, even here 

 the spiral band is not at first present, as in the small vessels, but the 

 secondary (or internal) membrane is studded with numerous minute 

 pores, giving to the vessels their reticulate appearance, similar to that 

 of the porous vessels of dicotyledonous plants. 



In conclusion, then, it is assumed that the metamorphosis of vessels 

 is confined to these points : 



