980 SUMMARY OF CUERENT RESEARCHES RELATING TO 



Boluble. The membrane which bounds the cytoplasm outwardly and 

 inwardly is not distinguishable chemically from the rest of its substance, 

 and is formed out of the cytoplastin. The cytoplastin is coagulable by hot 

 water, but is altogether insoluble in it. 



The following is a summary of the more important chemical reactions 

 of the substances above described : — The plastins (chloroplastin and cyto- 

 plastin) are insoluble in concentrated potash-lye and in a 10 per cent, solution 

 of sodium chloride ; while all the nuclear substances are soluble in these 

 reagents ; the plastins are not digested either by trypsin or pepsin, while 

 the nuclear substances are all dissolved, at all events by trypsin. Chloro- 

 plastin is distinguished from cytoplastin by swelling up strongly with a 

 1 per cent, solution of hydrochloric acid, by which the latter is precipitated ; 

 chloroplastin is insoluble, or swells up slightly in a 5 per cent, solution 

 of sodium phosphate, in which cytoplastin swells up strongly or is entirely 

 dissolved. 



Among the nuclear substances, chromatin and pyrenin are distinguished 

 by their great absorptive power for pigments ; their respective solubility 

 differs with various reagents; chromatin is rapidly, pyrenin only very 

 slowly digested by trypsin. Amphipyrenin absorbs pigments much less 

 rapidly than pyrenin ; it dissolves with difficulty in a 10 per cent, solution 

 of sodium chloride, while pyrenin is readily soluble in it; on the other 

 hand it is soluble in a 1 per cent, solution of potash-lye, pyrenin only with 

 difficulty. Linin and paralinin are distinguished by their strong power of 

 swelling with various substances, including water : paralinin is digested by 

 pepsin, while linin is not. Metaxin is distinguished from the plastins by 

 being digested by pepsin and trypsin ; and from the nuclear substances by 

 swelling up or dissolving in a 1 per cent, solution of sodium chloride, in 

 which the latter are completely insoluble. 



Position of the Nucleus in Mature Cells.* — Observations made by 

 Herr G. Haberlandt lead him to the conclusion that the position of the 

 nucleus in mature cells is not arbitrary, but depends on its function as the 

 bearer of the idioplasm which governs development, this idioplasm being 

 invariably seated in the nucleus. 



When any particular wall or part of a wall is more strongly thickened 

 than the rest, the nucleus is usually in immediate contact with this wall, 

 and is sometimes connected with it by a string of protoplasm. A good 

 example of this is the aquiferous epidermis of many orchids, where the 

 nucleus is usually in contact with the outer wall. In other cases, when 

 the inner wall is the thickest, it is in contact with it. In the guard-cells 

 of stomata it is invariably in apposition with the thickened ventral walls. 

 The rule is strikingly exhibited also in cells containing cystoliths. In the 

 branching palisade-tissue of some Eanunculaceae and of Samhucus, the 

 nucleus has a central position, and is connected with the thickened portions 

 of the wall by strings and plates of protoplasm. 



In young roots (Pisum sativum, Triticum vulgare) the root-hair originates 

 from a protuberance of the portion of the wall immediately over the nucleus, 

 or the young root-hair is connected with the nucleus by one or more strings 

 of protoplasm. In branched hairs it lies in their basal portion. 



In multinucleated unicellular plants (Saprolegnia, Vaucheria), branches 

 always originate immediately over a nucleus placed close against the cell- 

 wall. The process of regeneration which takes place in many species of 

 Vaucheria is always intimately connected with the presence of at least one 

 nucleus. 



* Ber. Deutsch. Bot. GeselL, v. (1887) pp. 205-12. 



