COURSE OF THE LATICIFEROUS TUBES. 435 



In ttie leaf-stalks and ribs of the lamina they follow the vascular bundles, often accom- 

 panying and touching sieve-tubes and vessels. In the parenchyma of the leaf they end 

 with numerous anastomosing branches. 



After the commencement of secondary thickening the root has a similar structure, and 

 a similar distribution of the laticiferous tubes to that In the stem. 



4. Among the milky Fapaveracesa two types of laticiferous tubes are to be dis- 

 tinguished. The one is represented by the investigated species of Papaver, Roemeria, 

 and Argemone, and shows tubes which arise from elongated elements, but only rarely 

 allow traces of the original qross-walls to be recognised in the mature condition ; 

 these are connected Into a net by more or less numerous anastomoses. In the stem 

 and petioles they lie in tangential curved rows in the phloem of the vascular bundles, 

 in each one of which they anastomose in the transverse direction, though there are no 

 anastomoses between those of the different bundles of an internode. In the (secondarily 

 thickened) root, in the cortical .parenchyma, and especially the bast layer, and also in 

 the parenchyma of leaves, pericarps, &c., they end in an abundantly ramified net.' 



The other type is represented by Chelidonium, and is characterised by the facts that 

 the cross-walls of the elements merely have one or more large perforations in the middle, 

 while on the other hand their edge remains preserved, and that reticulate connections 

 do not occur. On account of the partial persistence of the cross-walls, the tubes appear 

 at the first glance like rows of cells, the articulation of which comes out all the more 

 sharply, as they are usually somewhat constricted at the cross-walls (cf. Figs. 80, 81, p. 189). 

 Sometimes when two tubes are in direct lateral contact, perforations appear to occur 

 in the lateral wall also. In the older roots the tubes are often branched, owing to the 

 fact that a series of elements is continued from one point into tvro diverging series, which 

 meet at an acute angle ; and the individual elements are short, on the average z-4 times 

 as long as broad, being of about the same length as the neighbouring parenchymatous cells, 

 and elements of the sieve-tubes. In the parts of the plant above ground, on the other 

 hand, the elements are very elongated, so that their ends more rarely come into view 

 in preparations. In the (older) roots, the tubes in the bast-layer are so distributed in 

 groups, forming concentric, irregularly interrupted rows, that every group iisually lies in 

 the neighbourhood of a small group of sieve-tubes, surrounded by masses of parenchyma 

 containing starch. In the stems and petioles narrow laticiferous tubes lie scattered in 

 the vascular bundles within the phloem, and at the periphery of the xylem ; they further 

 occur externally to the vascular bundles, on the outside of the fibrous bundles bordering 

 on the phloem, and also, isolated in the peripheral (cortiqal) parenchyma. In the lamina 

 of the leaf and the parts of the flower the system of tubes ends in the reticulate form 

 described above for other cases. 



In other Papaveraceae, especially Macleya cordata and species of Glaucium (I investigated 

 Gl. luteum), no doubt also in Eschscholtzia (which, however, requires further investigation 

 with reference to the statement of the anonymous writer in the Botanische Zeitung, 

 1846), and in the Fumariaceae, no laticiferous vessels whatever are known. A red sap, 

 which is on the whole clear, and mixes both with water and alcohol without turbidity, 

 appears conspicuously on cut surfaces of the rhizome of Sanguinaria : it is contained in 

 large, thin-walled, roundish or shortly cylindrical cells or sacs, which are abundantly dis- 

 tributed through the whole parenchyma, sometimes isolated between (starch-containing) 

 parenchymatous elements, sometimes, and especially in the cortex, forming continuous 

 longitudinal rows (cf. Hanstein, /. c, Taf. I). In the stem and petiole, which I have 

 not investigated, these sacs are elongated cylindrical or prismatic. Neither their wails 

 nor their contents show the properties characteristic of laticiferous tubes ; they were 

 therefore mentioned above at p. 147. 



The same holds good for the sacs filled with a clear reddish-yellow sap, which are 

 scattered through the parenchyma in the root of Glaucium luteum, and which, according 

 to the form of the contiguous elements, are more or less longitudinally-extended.- In 

 the stem and foliage of species of Glaucium (cf. Tr^cul, I.e.) they are absent. In the 



F fa 



