202 D. H. SCOTT. 



very closely with that of M. Glaziovii. The above state- 

 ments may, therefore, probably be extended to the genus as a 

 whole without any great risk of error. ^ 



The results of my observations may be summed up as 

 follows : 



1. In Manihot the laticiferous tubes are not cells, as in the 

 members of the order Euphorbiacese hitherto investigated, but 

 vessels, agreeing in'most points of distribution, structure, and 

 development, with those of the Cichoriaccce. 



2. The high development of the laticiferous system is not 

 inconsistent with the presence of large, numerous, and well- 

 developed sieve-tubes. Hence, the prevalent views as to the 

 mutual substitution of these two classes of organs are, to say 

 the least, of limited application.- 



In conclusion, I may add one or two general observations 

 on the first of the two results just stated. The proof that in 

 one and the same natural order both articulated and non- 

 articulated laticiferous tubes may occur, shows that the struc- 

 ture of the tissue in question is of less importance as an '' ana- 

 tomical character" ^ than has hitherto been supposed. The 

 presence of laticiferous tissue is evidently a character which 

 has made its appearance repeatedly at distinct points in the 

 phylogenetic development of the Phanerogams. This follows 

 from the occurrence of the articulated tubes in groups so re- 

 mote from one another as the Cichoriacese, Papaveracese, and 

 Aroidese, and of the non-articulated tubes in, for example, the 

 Euphorbiacese and Asclepiadese. The results of the present 

 investigation seem to me to render it probable that even within 

 a comparatively narrow circle of relationship the development 

 of laticiferous tissue has had more than one starting-point. 

 In the order Euphorbiacese I should be disposed to assume a 



' la Holler's short description of the cortex of M. carthagenensis there 

 is no mention of laticiferous tissue (' Anat. d. Baumrinden,' p. 299). 



- I may mention Periploc'a as a further well-known example of the simulta- 

 neous presence of an extensire laticiferous system, and well-developed sieve- 

 tubes. 



3 Cf. 'DcBary/I, c, p. 27. 



