SPECIAL METHODS. 163 



yields, on oxidation with nitric acid, mucic acid ; on heating 

 with dilute sulphuric acid, galactose (C 6 H 12 O 8 ) and a penta- 

 glucose. It is also characterized by giving a cherry-red 

 fluid on heating with phloroglucin and hydrochloric acid, 

 while no color is produced in the cold. On heating, para- 

 galactan is transformed by \% hydrochloric acid or \% sul- 

 phuric acid into sugar, while cellulose is attacked only by 

 pretty concentrated solutions. 



It is an important fact for the microchemical recognition 

 of paragalactan that it is insoluble in cuprammonia and 

 prevents the solution of the cellulose which occurs in the 

 same membranes, while the latter is readily dissolved by 

 cuprammonia after the removal of the paragalactan by 

 boiling 2.5$ hydrochloric acid. Paragalactan does not seem 

 to be colored by chloroiodide of zinc ; at least, membranes 

 treated with this reagent showed only a slight bluing, while 

 the remains of the membrane are deeply colored after the 

 solution of the paragalactan. 



[This substance also shows the characteristics of the 

 hemicelluloses (cf. 285). The pentaglucose which it yields 

 besides galactose is probably arabinose, and it may there- 

 fore be called paragalacto-araban. It is very possible that it 

 is a mixture of two substances, galactan and araban.] 



c. Arabanoxylan. 



[287a. Schulze finds (II) a hemicellulose in wheat and 

 rye bran which yields, on hydrolysis, an arabinose and a 

 xylose, and may therefore receive the above name.] 



7. Callose, the Callus of the Sieve-tubes. 



288. Until recently the name callus was generally given 

 to a pretty strongly refractive substance which causes a 

 more or less complete closing of the sieve-poles in old sieve- 

 tubes, and finally covers the whole sieve-plate with a thick 

 mass. Mangin has lately recognized (I-IH) the more gen- 

 -eral distribution of this substance, especially in the mem- 

 branes of various pollen-grains and pollen-tubes and in 

 many fungi. It is, for instance, widely distributed in the 



