104 Mr. W. Gardiner, The Histology of the Cell Wall, 



give good results. The method of staining indirectly by washing 

 out may also be applied to endosperm tissues generally. The stain* cL 

 sections are best examined either in water or in very dilute glyce- 

 rine. I have as yet given little attention to the question of making 

 permanent preparations, although I have initiated certain experi- 

 ments which may possibly load to a satisfactory result. 



It is probable that the method in its present form will not be found 

 to be available for the study of adult lignified or suberised cells, 

 though up to the present I have made no observations upon such 

 tissues. The investigation of young tissue will, however, doubtless 

 give good results, and will establish that in them, also, the general 

 structure prevails. I am strongly convinced that the above method, 

 or similar methods, based upon "non-alcoholic" treatment, will be 

 found to be peculiarly suitable for the investigation of the tissues of 

 plants, and will in the future lead to observations of interest and 

 importance. 



A summary of results may now follow. 



As my new method owes its origin to a study of the cells of 

 endosperm I propose to deal with that tissue first. 



The present investigation entirely confirms and extends the 

 results I obtained in 1883.* At that time, however, many important 

 problems still awaited solution. In the first place, what was believed 

 to be the typical and universal structure could only be demonstrated 

 with particularly favourable material and in a limited number of 

 plants. Further, even in ripe seeds, where treatment with iodine 

 proved that connecting threads were present, special difficulties were 

 experienced when attempts were made to stain them with aniline 

 dyes. Lastly, for young se<eds the methods were quite unsuitable. 

 With the present methods we are in a position to investigate the 

 structure of endosperms generally, and to follow their development 

 even from the earliest stages. The more refined method also gives 

 more sure and satisfactory results. 



It is possible to make certain general statements concerning the 

 connecting threads of endosperm cells. In the first place, the his- 

 tological structure of endosperm establishes a point of great im- 

 portance which is only emphasised by the study of tissues generally, 

 viz., that in pitted cells the pit-closing membrane is invariably 

 traversed by threads. For descriptive purposes these may be called 

 " pit-threads." Threads may also be present which traverse the 

 general wall, and these may, similarly, be called " wall-threads." In 

 the somewhat exceptional cases of unpitted cells the thread system 

 is necessarily composed of " wall -threads " only. In many pitted 

 cells both " pit- threads " and " wall-threads " are present ; but in the 

 majority of cells the threads appear to be limited to the pits, 

 * Gardiner, ' Hoy. Soc. Proc./ No. 22$, 1883. 



