402 MR. G. 8. WEST ON 
Thus, if the plant be rotated through 180°, the force of gravity 
immediately causes the corpuscles to descend through the fluid in 
the vacuole until they arrive at its new base. These corpuscles or 
granules are of a faint yellow colour, and appear brown in a thin 
stratum ; but when present in immense numbers they sometimes 
give the plant a very dark (almost a black) appearance. 
The following is a complete summary of all the records of 
variation in the cell-contents of Desmids :— 
1. Spirotenia obscura, Ralfs. The structure and arrangement 
of the chromatophores described by Lütkemüller in Oesterr. 
botan. Zeitschr. xlv. 1895, pp. 2, 93, t. 1. ff. 1-6, 15-19. 
2. Penium "minutum, Cleve. Variability of chromatophores 
mentioned by Lütkemüller under the erroneous name of 
Docidium Baculum, Bréb. in Oesterr. botan. Zeitschr. xlii. 1893, 
p. 10, t. 2. ff. 9-15. (Cfr. remarks by West & G. S. West in 
Journ. Bot. vol. xxxiii. 1895, p. 65.) 
3. Cosmarium pyramidatum, Bréb. Variability of pyrenoids 
described by Lütkemüller in Oesterr. botan. Zeitschr. xliii. 1893, 
p. 6, t. 2. ff. 1-8. (Cfr. Nordstedt in Index Desm. p. 215.) 
4. Cosmarium sphagnicolum, West & G. S. West. Variations 
in chromatophores mentioned in Ann. Bot. vol. xii. 1898, p. 52, 
1f. 34-36. 
5. Cosmarium contractum, Kirchn. Variability of pyrenoids 
recorded by Lütkemüller in Oesterr. botan. Zeitschr. xliii. 1893, 
p. 8, t. 3. ff. 16-18.  Erroneously recorded by Lütkemüller as 
C. pseudoprotuberans, Kirchn. (Cfr. Nordstedt in Index Desm. 
p- 209.) 
6. Cosmarium ornatum, Ralfs. Variability of pyrenoids men- 
tioned by West & G. 8. West in Ann. Bot. vol. xii. 1898, p. 52. 
IV.— Variations in Conjugation. 
Few observations on the conjugation of Desmids have been 
recorded other than the mere mention of the occurrence of zygo- 
spores. I know of no instances of the occurrence of hybrids, and 
of few recorded instances of abnormal conjugation. The im- 
portance of this subject in its bearings on the classification of 
Desmids has not been sufficiently recognized, although it is a 
study which brings forward most interesting proofs of genetic 
relationship between many of these plants. It is also important 
in its bearings on the evolution of the Desmidiex, a few obser- 
vations on vagaries in the conjugation of Zyalotheca dissiliens 
