Observations on Spirogyra. 431 



appearance of crystals which are being dissolved. The 

 composition of the crystals seems to be oxalate of calcium, 

 as the crystals dissolve without evolution of gas in nitric 

 acid, and as they are insoluble in acetic acid. 



EXPLANATION OF PLATE IL 

 (Illustrating Mr Mann's papers on Chlorophyll and Spirogyra.) 



Absorption Spectra of Chlorophyll. 



1. Spirogyra, living chlorophyll. 



2. Moderately strong alcoholic extract from living material. 



3. Strong solution alcoholic extract from living material. 



4. Alcoholic extract evaporated and redissolved in benzole. 



5. Alcoholic extract from boiled material. 



6. Alcoholic extract from boiled material with ammonia added. 



7. Alcoholic extract from boiled material Avith nitric acid added. 



8. Extract made by triturating with benzole. 



9. Extract made by triturating with xylol. 



10. Extract made by triturating with petroleum ether. 



11. Average spectrum given by living plants. 



Fig. 1. a, Normal size of one cell of Spirogyra nitida during 

 summer, h, Increase during winter. 



Fig. 2. Jar cultivation of Spirogyra. a, Viewed laterally. 

 h, Viewed from the front, x, Lower part with equal growth of 

 S. nitida and S. jugalis. y, Middle part consisting largely of 

 S. nitida. z, Upper part consisting entirely of *S'. nitida. 



Fig. 3. Spirogyra jugalis. Cell with two nuclei and incom- 

 plete cell wall. 



Fig. 4. Side view of cell showing change in outline of two 

 chlorophyll-bands from deposition of starch. 



Fig. 5. Bag formed by fusion of the nuclear ends of the support- 

 ing threads. The nucleus has been removed. 



Fig. 6. Stages in starch formation, a-f, Surface view, a'-/', 

 Lateral view. 



Fig. 7. Spirogyra, sp., showing chlorophyll-bands forming a bag 

 round the nucleus. 



Fig. 8. a-h, Crystals. 



