IN VEGETABLE BIOLOGY. 599 



often to such an extent as to touch the latter. Professor Stras- 

 burger* doubts the accuracy of Tangl's statement ; he believes 

 that communication is maintained by groups of threads running 

 through the wall from pit to pit, but he is not quite satisfied 

 about the point ; and G-ardiner leaves matters in the same state. 

 The seeds sent me from Kew were, I suspect, from the same 

 sample as those which Gardiner-)- examined ; they were so old 

 and dry as to afford little chance of satisfactory examination ; 

 however I have sometimes seen the method of continuity shown 

 at fig. 8, and occasionally caught sight of fine threads running 

 concentric with and occupying the interval between the two 

 intramural threads there figured. The only doubt which I have 

 with regard to this species is whether the cell-walls themselves 

 be not penetrated by threads. Treated with water both primary 

 wall and secondary layers swell up greatly, the former especially 

 at the angles, the latter to differentiate into an inner many- 

 striated zone, and an outer one marked by a great number of 

 minute dots ; the striation of the inner zone is continued along- 

 side the canals where they are present (fig. 9). If a section is 

 placed in a drop of solution of iodine in alcohol upon a slide for 

 a minute or two, and a cover-slip being put on, is then carefully 

 irrigated with water, in some part of the section the dots just 

 referred to may appear in the form of interrupted lines which 

 seem to radiate on all sides, from the lumen to the circumference 

 of the cell. Whether, however, these be cords of intercellular 

 communication or small rifts occurring only in old seeds, or, as 

 they sometimes seem to be concentrically disposed, merely inter- 

 rupted striae of the layers of thickening, I am quite unable to 

 decide. 



The cells of the horny endosperm of S. spinosa swell up so 

 much in water that the lumen is frequently all but obliterated ; 

 the layers of thickening differentiate in water into two sharply- 

 defined zones, a narrow inner strongly, and a wider outer faintly, 

 striated one. Through the walls of cells treated with iodine in 

 alcohol and partially swollen up in water continuity can be made 

 out if care and patience be brought to the examination ; it is, 

 however, a matter of difficulty to see the threads, the remarkable 

 striation of the wall greatly impeding the view of them (fig. 10). 



* • Teber den Ban und das Wachsthum der Zellhaute.' 

 + Phil. Trans, memoir. 



