DEVELOPMENT OF ARTICULATED LATICIFEHOUS VESSELS. 139 



vessels or end blind. These line ramifications, termed 

 capillary tubes by Schacht, are said to traverse the inter- 

 cellular spaces. Connecting tubes are also formed in the 

 parenchyma of the medullary rays, which are said to arise 

 from the fusion of cells, and to establish a communication 

 between all the vessels. In the cortex only lateral 

 branches from the main trunks are said to occur. 



Schacht's observations also extended to various other 

 plants, of which Sonchus has most interest for us. In this 

 case Schacht has not much to say about the actual develop- 

 ment. His words are,^ " The process of the fusion of cells 

 to form the laticiferous vessels seems to be the same here as 

 in Carica, with the one difference that the parenchyma cells 

 of the medullary rays take part in the process much more 

 rarely here than in the other case,''' &c. It is scarcely to be 

 inferred from this that Schacht had really traced the devel- 

 opment, nor do the figures which he gives ^ show anything 

 of the origin from cells. On the other hand, the mode of 

 lateral union between the vessels is correctly represented. 

 They here send out lateral protrusions which meet those of 

 other vessels, and establish a connection in a way similar 

 to the process of conjugation in Spirogyra, &c. 



There can be no doubt that this work of Schacht's marks 

 an important advance in our knowledge of these organs. 

 Schacht himself still struggled to save his Bast-cell theory, 

 asserting that true bast-cells also undergo fusion,^ but his 

 position could no longer be regarded as tenable. 



During the next few years comparatively little of interest 

 was published on the laticiferous organs. In 186S Hartig'* 

 recognised for the first time the distinction between articu- 

 lated and inarticulated laticiferous vessels. Among the 

 former he mentions the Cichoriacese and Papaveraceae, as 

 well as the Acerinese, which are no longer considered as 

 possessing true laticiferous vessels. Those of the Euphor- 

 biacea3 are described as inarticulated. The distinction thus 

 rightly introduced was not generally accepted till much 

 later. 



In the following year (1863) the knowledge of our sub- 

 ject was further extended by the publication of VogPs ' 

 researches on the laticiferous vessels of two plants belong- 

 ng to the Cichoriaceae. He ob served the development of 



^ Loc. cit., p. 524. 



2 Loc. cit., figs. 11—13. 



^ Loc. cit. p. 530. 



* ' Botan. Zeitung,' 1862, p. 97. 



'" ' Sitzungsberichte der Wiener Akademie,' vol. 43 B, p. 668. 



