438 The //{(>/>;/ >/ /(/" (.',// ',///, tr. 



in the outer or free walls of the epidermis, so that diffusion only (as 

 opposed to direct transference) can take place l>etween the cell con- 

 tents of the endosperm and those of the cotyledon. 



In the stomata of the cotyledon threads have been seen in a few 

 cases connecting the guard cells with the epidermal cells. 



The parenchymatous tissue all over the seedling plant shows con- 

 necting threads of a similar character. In the end walls of the cells 

 they occur irregularly scattered, but in the lateral walls they are 

 usually in isolated groups, mainly in consequence of the growth in 

 length which these walls have undergone, and are also "situated in 

 shallow pits. 



The palisade cells of the cotyledon, which at first are united together 

 in all directions, very soon separate, forming plates of tissue, and the 

 threads in the walls along which separation takes place are very 

 quickly obliterated. A similar obliteration of threads is seen to occur 

 in those walls of pericyclic cells which are situated between the 

 living cells and the young transfusion cells in process of lignification. 



The living cells of the pericycle, which are richly connected together 

 by threads, form the passage cells from the cortical tissues to the 

 phloem, and between these cells and the sieve tubes come the albu- 

 minous cells, which possess thread groups occurring in localised thick- 

 enings of their walls. The threads, which are long and usually curved, 

 stain in a peculiar manner, and appear to have an important function 

 with reference to the passage of material from the mesophyll to the 

 phloem. 



The phloem tissues of the seedling of Pinus pinea present a distinct 

 type, the peculiarities of which are treated of at some length. The 

 large cells of the outer portion are characterised by long oblique end 

 walls full of threads; whilst the thick- walled cells of the inner part 

 possess square end walls traversed by numerous long threads, re- 

 sembling the sieve tubes of dicotyledons. As development proceeds, 

 sieve tubes like those of the adult tissues are, however, quickly 

 developed from the cambium. All the sieve tube threads show a 

 characteristic median dot. 



The root cap of the seedling root shows numerous threads connecting 

 its cells together, and also affording communication both with the free 

 surface of the root as well as internally with the cells of the periblem. 

 The function of the root cap as an organ for stimulus perception and as 

 an absorbent organ is considered with reference to the abundance of the 

 connecting threads. 



In Pinus sylwslris the characters of the threads in the cortical tissues 

 of the adult stem and root are similar to those of the seedling. 

 Threads occur, however, in the radial and end walls of the cells, but in 

 the cells just under the cork they are distributed in large numbers in 

 the tangential walls, and this change in the main direction of the 



