DEVELOPMENT OF ARTICULATED LATICIFEROUS VESSELS, 149 



also holds good of the hypocotyl — at any rate in its 

 lower part. The hypodermal vessels contain latex when no 

 signs of it are to be found in those of the plerome. And, 

 further, the fusion of the cells is far advanced in the former 

 at a time when it has scarcely begun in the latter. This 

 distinction, however, does not hold good in the cotyledons. 

 Here the development is uniform at all parts of the same 

 cross-section. 



With reference to the actual process of cell fusion I have 

 obtained the following results : — The wall which is to be 

 absorbed first appears somewhat swollen ; the swelling, how- 

 ever, is not very marked. Then the membrane begins to 

 dissolve gradually at some one point. Probably a middle 

 lamella is present which resists solution longest, for stages 

 are often found where the perforation is still closed by an 

 extremly thin membrane. The opening is at first very 

 small ; it often,'but by no means always, occupies the centre 

 of the cross-wall. It increases gradually in size, and before 

 the cross-wall has quite disappeared the contents of the two 

 cells become continuous. As regards the lateral perforations 

 I have only to confirm Schmalhausen^s statement, that they 

 are habitually formed in the neighbourhood of a cross - 

 wall. 



The observations on Tragopogon which I have just 

 described were partly repeated on Scorzonera hispanica. 



Here also the rudiments of the laticiferous vessels can be 

 recognised in the ripe seed. The process of their develop- 

 ment is essentially the same as in Tragopogon. Even before 

 the cross- walls are absorbed the cells become distinguishable 

 from the others by their contents, and no doubt already 

 contain latex. The distribution is somewhat different in 

 the two plants. In the seedling of Scorzonera almost all the 

 laticiferous vessels belong to the phloem part of the fibro- 

 vascular bundle, only in the cotyledons some are found iso- 

 lated in the cortical parenchyma near the epidermis. In 

 one other point Scorzonera differs from Tragopogon ; in the 

 former the outgrowths from the latex vessels, which after- 

 wards establish communication between the main trunks, 

 are formed at an early stage of germination. We have 

 already seen that these outgrowths appear to be wanting in 

 the seedling of Tragopogon. This mode of connection 

 between the latex-vessels is best observed in the neighbour- 

 hood of the growing point of the stem in older plants of 

 Scorzonera, and especially in their young leaves. Here it is 

 easy to find vessels in which the articulations are still clearly 

 distinguishable (fig. 8). These young vessels send out 



