206 



EOT A NIC A L MICR O 7^E CHNIQ UE. 



singly or in twos or threes in each leucoplast (cf. Fig. 42, /). 

 But, since the leucosomes are soluble in water 



/Ol and very sensitive to the most various reagents, 



^^ / it is better to use, as a rule, fixed and stained 

 material. 



The best method is to fix sections from the 



FIG. 42. Leuco- . 



piasts from the living objects in a concentrated alcoholic solu- 



epidermis of < 



the upper sur- tion of corrosive sublimate, and, after washing 



face of the leaf 



of Tradescan- ( c f. 3io), to stain by the acid fuchsin method 



, tta discolor, t, ^ v ^ ' ' 



leucosomes. g. jf the washing is stopped at the right 

 moment, the leucosomes alone are deeply stained. 



c. Pyrenoids. 



361. The starch-centres or pyrenoids observed in the 

 chromatophores of various Alg& and of Anthoceros consist 

 of a central portion of proteid and a starch-envelope sur- 

 rounding it. 



The most essential part of the pyrenoid, the proteid nu- 

 cleus, appears often to possess a more or less regular crystalline 

 form (cf. Fig. 43, 2), according to Schimper's observations 

 (III, 74). On the other hand, it is certain that non-crystal- 

 line pyrenoids also occur, as in case of the one shown in 

 Fig. 43, 3, which probably represents a stage in fission (cf. 

 Zimmermann I, 48). Similar forms have lately been ob- 

 served by Klebahn (I, 426) in Cosmarium. 



362. In the presence of large quantities of starch, the 



7> 



FIG. 43. i, part of a chromatophore of Spirogyra sp. ; 2, chromatophores of Cladophora 

 sp.; 3, constricted pyrenoid of Zygnema sp. after fixing with picric acid and staining 

 with acid fuchsin ; /, pyrenoid ; s, starch-grains ; z, nucleus ; , nucleolus. 2, after 

 Schimper. 



proteid nucleus of the pyrenoid is only with difficulty or not 

 at all to be recognized within the living cell. Then the use 

 of suitable staining media is to be recommended. The py- 



