DEVELOPMENT OF ARTICULATED LATICIFEROUS VESSELS. 143 



into actual vessels during germination by means of the 

 absorption of the cross-walls and portions of the side-walls. 

 This process is said to begin at the root end and thence to 

 advance to the opposite end of the embryo. The distribu- 

 tion of the laticiferous organs in the embryo resembles that 

 among the Euphorbiacese. In both cases they form two 

 systems, one of which belongs to the Periblem the other to 

 the Plerome. The laticiferous vessels have nothing in 

 common with the sieve-tubes either as regards development 

 or structure. I reserve details for the second part of the 

 paper. 



The ' Vergleichende Anatomie ' of De Bary contains, 

 in addition to valuable original observations, a summary of 

 the results of all researches on the subject previous to 187T. 

 This may be regarded as pretty exactly representing the 

 present state of the question, as very little new information 

 has been gained since that year. The conclusion at which 

 one must arrive is that the development of the articulated 

 latex-vessels by cell-fusion may be regarded as established 

 with approximate certainty, but nevertheless, that the pro- 

 cess has only been directly observed in very few cases.^ 



Since 1877 only one work has appeared which requires to 

 be noticed here. This is E. Faivre's ^ investigation of 

 Tragopogon porrifolius. The author asserts that the ripe 

 embryo of this plant consists essentially of parenchyma 

 containing abundant protoplasm, neither tracheae nor lati- 

 ciferous vessels being as yet developed. The former are 

 said to show themselves first, but even they only after the 

 root has protruded from the envelopes of the seed. The 

 laticiferous vessels he finds to be developed by the fusion of 

 rows of cells, and this mode of origin could often be 

 detected subsequently by means of the evident articulations. 

 The latex-vessels were found in the greatest numbers in the 

 cotyledons. Faivre also has observed the two ways in 

 which neighbouring vessels are connected, by the fusion of 

 transverse rows of cells, and by outgrowths. As regards the 

 distribution, Faivre finds that an intimate relation exists 

 between the tracheoe and the laticiferous vessels, although 

 they are never in communication. The latex itself is said 

 not to appear until the root has attained a length of several 

 millimetres, I shall soon have an opportunity of showing 

 how far I have been able to confirm Faivre's statements by 

 my own observation. 



The investigations which I am now about to describe 



1 See De Bary, loc. cit., pp. 199 and 203. 

 =* • Comptes Rendus,' t. 88, 1879, p. 269. 



