142 1). H. SCOTT. 



each sends out branches towards the other, which arise as 

 protrusions. They grow between or even through the cells 

 of the intermediate tissue until they meet and inosculate. 

 In Tragopogon pratensis Trecul observed branches of this 

 kind^ which attained a length of 1*15 mm. 



Among the Aroidese^ Trecul seems to have observed both 

 the absorption of the cross-walls and the communication by 

 means of lateral branches in various species of Caladium. 



In another passage" Trecul calls attention to the fact that 

 in the Euphorbioe no trace of the origin from cells is to be 

 perceived, and is thus the first after Hartig to observe the 

 distinction between the articulated and inarticulated 

 vessels. 



More detailed accounts of the development are not to be 

 found in Trecul's treatises. 



The next work of importance on this subject, that by 

 David (1872), is occupied with the inarticulated latex-cells. 

 To him belongs the credit of finally establishing the dis- 

 tinction between the two classes of laticiferous organs, 

 although he failed to discover the true mode of development 

 of those which are inarticulated. He supposed that new 

 latex-cells are constantly being formed in the meristem of 

 the growing point, and, consequently, that a great number of 

 these cells, which have been developed successively, exist in 

 the mature plant. It is now knoAvn that the latex-cells are 

 formed, once for all, in the embryo, and in very small num- 

 bers (in some cases six), and that the whole laticiferous 

 system of the plant consists exclusively of the abundant 

 ramifications of these few original cells. This discovery was 

 first made by Schmalhausen^ (1877), and afterwards con- 

 firmed by the researches of Weber in the Wiirzburg 

 Laboratory. 



Schmalhausen's work is also of great value as regards the 

 development of the articulated laticiferous vessels. His 

 observations on the mode of origin of these organs in the 

 Cichoriacese seem to me to bo by far the most accurate that 

 we possess. In describing my own observations I shall 

 often have occasion to refer to his statementSj so that only 

 his main results need be mentioned here. Schmalhausen 

 investigated the embryos of Tragopogon and Scorzonera. 

 He found that the rudiments of the laticiferous vessels exist 

 in the embryo of the ripe seed, and that they are converted 



• ' Comptes Rendus,' t. 61, p. 1163. 

 ° Ibid., t. 60, p. 131-9. 



3 'Beitriige zur Kenntiiiss der Milclisaftbehalter der Pflanzen,' St. 

 Petersburg, 1877. 



