368 SUMMARY OF CUKRENT RESEARCHES RELATING TO 



(Hcqjlophyllum), Urticaceae {TJrticci), aucl Palmse (Nunnezharia and 

 Phoenix). 



In Euphorbia Tirucalli they are unusually beautifully developed. 

 In an early stage a centre of formation may be observed, wbicli may 

 be a chlorophyll- or starch-grain ; round this is formed a massive 

 nucleus, to which the crystals are attached with a radiate arrangement. 

 Subsequently they exhibit evident stratification. The radiate portion 

 is at first colourless, afterwards yellowish brown ; the whole is 

 evidently crystalline. The sphero-crystals are usually readily 

 soluble in cold water ; their behaviour towards reagents is similar to 

 that of inulin. 



In Urtica major the sphero-crystals are found in the guard-cells of 

 the stomata and neighbouring cells, less often in the fundamental 

 tissue. They are dark brown, insoluble in cold or in boiling water, 

 and appear allied in their nature to hesperidin. 



In Nunnezharia they occur in the peripheral fundamental tissue 

 of the stem, forming large yellow clusters, also in the leaves, bracts, 

 and rachis of the inflorescence. They are slowly soluble in cold 

 water, and exhibit the closest resemblance to inulin. 



Structure of Starch-grains.* — A. Meyer discusses Nageli's theory 

 of the formation of starch-grains by intussusception, and A. f". W. 

 Schimper's "]■ that they are sphero-crystalloids of a carbohydrate formed 

 by apposition of concentric layers ; and argues in favour of the latter, 

 from the similarity of the phenomena they present to those of arti- 

 ficially prepared sphero-crystals of a carbohydrate such as sugar. 

 In these the three following characters are found, which agree with 

 those of starch-grains : — (1) Variations in the external conditions 

 which affect crystallization cause also the formation of layers ; (2) the 

 centre of crystallization is less dense than the surrounding layers ; 

 (3) the youngest external layer is the densest, the density of the suc- 

 cessive layers towards the interior decreasing with their age, 



A full description follows of the starch and starch-generators in 

 the rhizome of Iris pallida and germanica, the following being the 

 general conclusions arrived at : — (1) The starch-generators in the 

 rhizome of Iris only perish with the death of the cells in which they 

 are found ; (2) in them not only the formation but the solution of 

 starch-grains takes place ; (3) both internal and external solution of 

 the starch-grains takes place in the cells; (4) the only simple 

 explanation of all the phenomena observed is presented by the hypo- 

 thesis that the starch- grains increase in substance by apposition. 



Assimilating Tissue.:]: — G. Haberlandt supports the view of 

 Schwendener that the structure and arrangement of the cells which 

 constitute the assimilating tissue are dependent on the process of 

 assimilation. The more important cell-forms of which it is composed 

 may be classified as follows : — 



* Bot. Ztg., xxxix. (1881) pp. 841-6, 857-64 (1 pi.), 

 t See this Journal, i. (1881) pp. 481, 909. 



X rritigsbeini's Jahib. fur wiss. Bot., xiii. (1881) pp. 74-188 (G pis.). Cf. this 

 Journal, i, (1881) p. 912. 



