153 D. H. SCOTT. 



parent, and for this reason it can iiere be easily demon- 

 strated that each of the cells has a nucleus. Treated with 

 heematoxylin these nuclei become just as clear as those of 

 the parenchyma cells, which they resemble in every respect. 

 They have a lenticular form, and are closely applied to one 

 of the side-walls of the celL Each has a fairly large nu- 

 cleolus. The nuclei persist throughout life. I have found 

 them in old latex-vessels which were beginning to become 

 disorganised. 



The parenchyma cells of the secondary cortex contain a 

 quantity of compound starch grains, which are formed as 

 soon as the cells have passed out of the cambial condition. 

 In the young latex- vessels starch grains are entirely absent 

 from the first, which makes it very easy to distinguish them 

 at an early stage. 



There is also one point in the distribution to which I will 

 call attention. I have often convinced myself that latici- 

 ferous vessels also occur in the xylem of the root, and that 

 not only in the medullary rays, but actually among the 

 tracheae. This is not invariably the case, but it is very 

 frequent. I must therefore express my disagreement with 

 Hanstein's assertion that in the Papaveraceae " no true lati- 

 ciferous vessels penetrate between the crowded cells and 

 vessels of the xylem bundle."^ Hanstein was of the opinion 

 that the pitted vessels which are often found filled with 

 latex had been mistaken for true laticiferous vessels. I 

 have myself often seen pitted vessels in this condition. 

 Their strongly thickened pitted walls bear no resemblance 

 w^hatever to those of the real latex-vessels. In size and 

 other characters they are also entirely different, so that con- 

 fusion could hardly take place between them, even if the 

 contents were " strongly coloured," which in the vessels in 

 question was not the case. The latex-vessels are always 

 much less numerous in the xylem than in the phloem. 

 Sometimes, but extremely rarely, they are in immediate 

 contact with the trachese. 



The results of my very fragmentary observations may be 

 summed up as follows : 



1. It has been shoAvn by direct observation that the lati- 

 ciferous vessels of the plants investigated arise from rows of 

 colls, of which the cross-walls, and, where two vessels are 

 in contact, parts of the side-walls are gradually absorbed. 

 The absorption takes place, as a rule, very early — in the 

 seedling, for example, during the first stages of germination ; 



> Loc. cit., p. n. 



