34 



NUCLEUS. The character of the Nucleus affords important distin- 

 guishing marks for the determination of species : its color ; the mark- 

 ings on its surface; the number of spirals (generally constant in each 

 species) ; the prominence of the ridges or its smoothness ; the mark- 

 ings on the shell wall, all are to be considered. 



The spirals, due to the twisting of the enveloping tubes, may be 

 marked by* prominent ridges, or the union between the enveloping 

 cells maybe a mere line and the Nucleus maybe quite smooth; if the 

 enveloping cells complete one circuit, then five striae are visible ; if 

 two or three turns, then ten or fifteen striae. 



At the lower end of the Nucleus, where the enveloping tubes 

 join the pedicle, spines often project, five in number, formed by the 

 extension of the woody formation between the enveloping tubes ; at 

 the upper end a single prominent spine is sometimes formed in a sim- 

 ilar manner. 



The contents of the enveloping tubes consist of a series of gran- 

 ules, at first green, but becoming colored, in some species, yellow or 

 scarlet (Ch. crinita), or red (Ch. coronata). In the coronula of Chara 

 the cells continue green, but in the Nitellae the cells of the coronula 

 remain colorless. 



In most species of Chara a calcareous shell forms between the hard 

 inner shell and the soft outer part of the capsule. This calcareous 

 layer is developed in a gelatinous network lying next the woody 

 shell and seems to be formed by the protoplasm of the enveloping 

 cells; in this mesh lime is deposited. 



This shell may persist long after the woody part has disappeared, 

 and is found in fossil nuclei, always with an opening at one end, 

 for the cell of the pedicle deposits no lime. No lime is deposited in 

 the coronula and this is never found in a fossil state. 



Characeae growing in water which contains much lime frequently 

 obtain an external coating of lime, but this is not a constant character 

 of any species and is not a true calcareous layer. 



A peculiar, abnormal development of the spore and its capsule, is 

 not infrequently seen, which consists of the complete absence of all 

 woody formation next the spore. In consequence of this the spore 

 swells up and becomes filled with a large amount of starch, and looks 

 like a round white globule filled with chalk. These abnormal sporo- 

 pliydia have been seen in a large number of species, especially of 

 Chara, and must not be taken into serious consideration in the deter- 

 mination of the species. 



In 1856 Braun presented to the Berlin Academy a communication 

 concerning Parthenogenesis in plants, especially in Ch. crinita. Male 



