DEVELOPMENT OF ARTICULATED LATICIFEROUS VESSELS. 145 



bundles enter the colylcdoniuy sheath their latex-vessels are 

 invariably connected with the hypodermal vessels by means 

 of cross branches. Similar connections occur repeatedly 

 in other parts of the sheath. In the cotyledons the latex- 

 vessels usually accompany the fibro-vascular bundles, which 

 are here much ramified, though here also isolated latex- 

 vessels occur. I have never been able to trace these vessels 

 into the growing point of the germ-stem above the youngest 

 leaves, but have always found them continued into the 

 young leaves themselves. It appears, therefore, that the 

 laticiferous vessels, like the fibro-vascular bundles, are never 

 cauline (stammeigene in Nageli's sense). 



The arrangement just described exists very evidently in 

 germ plants with the root protruding about five millimetres 

 from the seminal envelopes. The first question to be 

 settled is at what stage the differentiation of the organs in 

 question first begins. With reference to this point I have 

 investigated the like embryo in the dry seed. In a cross- 

 section (through the cotyledonary sheath, for example) (fig. 

 2), in the position where the hypodermal vessels ai-e always 

 found at a later stage, cells are here and there to be 

 detected which are immediately distinguishable from their 

 neighbours by their smaller size. In the radial direction 

 they are only half as wide as the ordinary parenchyma 

 cells. Seen in cross-section they always appear two to- 

 gether, and are commonly separated from the epidermis by 

 a single layer of cells. In a longitudinal section (fig. 3) we 

 find that these cells form longitudinal rows, and have evi- 

 dently been formed by the division of cells of the third 

 layer from the surface by means of tangential walls. It is 

 the outer of these two narrower rows of cells from which 

 the hypodermal latex-vessels are developed. Even at this 

 early stage a diff'erentiation of the cell-contents appeared to 

 me to be perceptible, as the cells in question contain only a 

 few small aleurone grains, while the latter are present in 

 great abundance in the parenchyma cells. ^ 



The rudiments of the fibro-vascular bundles also exist in 

 the embryo. Here, however, I was not able to distinguish the 

 latex-vessels in their earliest stage of development from the 

 other cells of the procambium.^ It was for this reason that, 

 in studying the first origin of the former, I turned my atten- 



1 This deficiency in aleurone grains extends more or less to the sister-cells 

 of the rudimentary lalex-vessels. Where lliis is the case it is possible 

 that two latex-vessels were to be formed side by side, which is not at all 

 unusual. 



* Cf. Schmalhausen, loc. cit., n. 23. 



VOL. XXII. NEW SER. K 



