38 



ment of regular individual forms. It is but natural that 

 the formation of the calcium- oxalate crystals is greatly 

 retarded or entirely ahsen* in the culture of seedlings in 

 media free from calcium. Cysoliths behave like crystals, 

 their normal development being conditioned by the calciui^ 

 supply. If this is lacking, according to Charyre^ only the 

 stem of the cystolith v/ill be deposited, the formation of the 

 cellulose head being omitted. Cystoliths are scantily 

 formed in leaves sufficiently exioosed to the light. ^ Hence, 

 as in the cases reported above, a lowering of the transpir- 

 (41) ation seems to be determinative; at least I have obtained 



rudimentary cystoliths in leaves of Ficus elastica . if trans- 

 piration -was arrested, even v/ith a continuous exposure to 

 light. Etiolated leaves of Acanthaceae form normal cysto- 

 liths, while, under the same conditions, in Moraceae and 

 Urticaceae these remain rudimentary. The calcium incrusta- 

 tions are arrested by lack of light. The hairs of the Bor- 

 ragineae also remain poor in calcium in etiolated speci- 

 mens, (according to Chareyre.) Melnikoff reported cystoliths 

 free from calcium. ^ 



g.BIFFERMTIATIOIT OF THE TISSUE 



An arrestment of tissue differentiation occuss in all 

 those oases in which the elements of certain cell complexes 

 develop in the same way as contrasted with the fact that 

 under normal conditions , certain individual cells or cell 

 groups would be formed differently from adjacent ones. .Hy- 

 poplasia is thus shown, in that a homogenous tissue is pro- 

 duced, where under normal conditions v/e find one composed of 

 well-differentiated layers and groups. It is evident that 

 this kind of hypoplasia cannot find expression in all organ- 

 iisras. We must at once exclude the unicellular organisms, 

 which do not live in colonies, and the multicellular ones 

 composed only of similar cells. As is well knov/n, however, 

 in most multicellular plants,- even in the algae and fungi, 

 an evident tissue differentiation is recognizable. 



Before we pass to these, a few words are necessary con- 

 cerning unicellular organisms . Only those come under our con- 

 sideration which are united into colonies with easily dis- 

 tinguishable components, as, for instance, many of the plank- 

 ton diatoms which form chains , the end member of each chain 

 often being differentiated from the others. Colonies of 

 0cendesmus caudatus behave similarly; their end cells are 



1. S. L'origine et la formation trichomatique de quelques 

 cystoliths. C. R. Acad. Sc. Paris, 1883, T. XCIII , p. 1073, 

 Sur la form. d. cystol. et leur resorption. Ibi4. , p. 1594. 

 louv. Hech. s. 1. cystol. Rev. d, Sc. Uat, , Montpellier ,111 , 

 Serie, T. Ill, p. 523. 



2. Ficus elastica according to Kohl, loe, cit. p. 39 



3. Untersuch. ub. d. Sorkommen d, GaCOs in Pfl. Disserta- 

 tion Bonn, 1877, p. 35. Compare with this also Kohl, loc. cit. 

 p. 141, and the observations of Mollisch on Cystoliths nor- 

 mally free from c ale iuip (Qest. Bot. Zeitschr. , 1892, Bd. 

 XXXII, pv 345.1 



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