230 SUMMARY OF CUERENT RESEARCHES RELATING TO 



Nucleus of the Cells of Secreting Tissue.* — L. Guignarcl has 

 paid special attention to the constitution of cells containing raphides 

 or other special substances. In the Cycadeee there are a number of 

 cells in the fundamental parenchyma of the stem and leaves which 

 contain crystals that often inciease in size until they occupy nearly 

 the whole cavity. Even when the crystal has attained its full size 

 the deformed nucleus can still be detected, though almost unrecog- 

 nizable from the pressure to which it has been subjected. In the 

 gum-passages which are distributed through the parenchyma, the 

 cells with delicate walls which surround the cavity contain copious 

 protoplasm in which a nucleus may be discovered, usually applied to 

 the internal wall. 



Among Coniferse, the cells which border the secreting canals are 

 also very active. The nucleus can readily be made out in the proto- 

 plasm, by the side of the globules of oleoresin. The same structure 

 characterizes the cells of the secreting canals of Umbellifera9, 

 Araliacese, &c. 



With regard to the sieve-tubes of Vitis, Cucurbitacese, &c., the 

 long cells which form them, and which communicate with one another 

 through their pores, retain their nuclei. When the callus which is 

 formed in winter has not closed the pores, the protoplasm accumulates 

 in the upper part of the cell, and even projects, through the perfora- 

 tions, into the superposed cell ; the nucleus is attracted by it, and is 

 sometimes found high up on the lateral wall, sometimes in contact 

 with the sieve. 



The nucleus does not appear to divide in the laticiferous cells of 

 Asclepiadcfe, Urticacese, &c. 



Analysis of Vegetable Tissues.| — E. Fremy classifies the con- 

 stituents of vegetable tissue under the following seven heads, the 

 characters being derived from their chemical constitution : — (1) Cellu- 

 lose-substances (cellulose, paracellulose, and metacellulose) ; (2) 

 Vasculose ; (3) Cutose ; (4) Pectose ; (5) Calcium pectate ; (6) Nitro- 

 genous substances; (7) Mineral constituents. The following are 

 some of their distinguishing characters. 



1. Cellulose-suhstanees. In this group are included all those 

 constituents of vegetable tissues which dissolve without colouring in 

 bihydi'ated sulphuric acid, producing dextrin and sugar, which are 

 not sensibly altered by alkaline solvents, and which resist for a long 

 time the action of energetic oxidizers. Schweitzer's reagent enables 

 at least the three following varieties to be distinguished : — (1) Cellulose. 

 Dissolves immediately in the copper reagent. This constitutes the 

 larger part of cotton-hairs and of the utricular tissue of certain fruits. 

 (2) Paracellulose. Dissolves in the copper reagent only after the 

 addition of an acid. This constitutes the utricular tissue of certain 

 roots and the epidermal cells of leaves. (3) Metacellulose. Insoluble 

 in the copper reagent even after the addition of acids. It occurs 

 principally in the tissue of fungi and lichens, and in the "fungine" 

 of Braconnot 



* Bull. Soc. Bot. Fiance, xxviii. (1881) pp. .S32-3. 

 + Aqu. Sci. Nat. (Bot.) xiii. (1882) pp. 353-9. 



