144' D. H. eCOTT. 



were undertaken at the suggestion of Professor Sachs, with 

 the object of investigating the development of the latici- 

 ferous vessels in certain instances somewhat more closely, 

 and as far as possible by direct observation. I have endea- 

 voured to avoid mere conclusions from analogy with refer- 

 ence to the development, such as are so frequent in most of 

 the former investigations, except those of Schmalhausen 

 and De Bary, and to rely only on successful thin sections. 

 The following statement, therefore, refer exclusively to 

 quite clear and unmistakeable objects, such as only thin 

 sections can afford. 



2. Original Observatiofis. 



I will first describe the development of the laticiferous 

 vessels in the germ plant of Tragopogon eriospermus, as I 

 have investigated this object more minutely than any other, 

 and germ plants generally have hitherto been examined by 

 very few observers with reference to this question. It Avill 

 first be necessary to describe shortly the distribution of 

 these vessels in the seedling. 



In the root of the seedling there are two distinct systems 

 of laticiferous vessels. First, scattered and not very nume- 

 rous vessels traverse the cortical parenchyma. They lie 

 pretty close to the surface, commonly in the fourth or fifth 

 layer of cells. Secondly, fhe axial cylinder possesses a 

 number of latex-vessels, which belong to the phloem, and, 

 as corresponds to the diarchic structure of the root, form 

 two large opposite groups, each of which occupies about a 

 quarter of the circumference. In the hypocotyl the latici- 

 ferous vessels preserve the same general arrangement (fig. 

 1). Here, however, the hypodermal vessels are much more 

 numerous than in the root. They lie still closer under the 

 epidermis, from which they are frequently separated only by 

 a single layer of cells. These vessels may be either isolated 

 or lie two or more together. The latex-vessels of the fibro- 

 vascular system assume a distribution corresponding to the 

 stem structure. Here, namely, they lie chiefly on the outer 

 (phloem) side of each bundle, though they also occur in the 

 interfascicular tissue. 



In the node the fibro-vascular bundles and the latex- 

 vessels belonging to them bend outwards into the cotyledon 

 so that they come to lie nearer the surface in the cotyledo- 

 donary sheath than in the hypocotyl. The hypodermal 

 vessels, on the contrary, preserve a direct course in entering 

 the cotyledons. At the point where the fibro-vascular 



