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another is emitted, generally of a spheroidal form, and about the same 

 time an exceedingly minute pellucid fibril is emitted from its posterior 

 end. 



" The first indication of the formation of a new cellule is the 

 emission of a small ovate body from the anterior end of the previously 

 formed one : at first it is almost colourless, and appears like a mere 

 exudation of sap ; as it advances, its almost liquid surface is gradually 

 changed into a greenish pellicle, and the cellule then swells into a 

 spheroidal form ; but this form is very soon altered when in its turn 

 it has protruded a new cellule. This last, originating on the convex 

 apex of the preceding (from which it appears to draw the liquid ne- 

 cessary for its own formation), is during its enlargement gradually 

 drawn closer and closer to the other, the convex end of which finally 

 becomes concave as the two surfaces approximate and form the par- 

 tition between one cellule and another. 



" The manner in which the cellules increase varies in different 

 species. In some a single cellule is emitted from the primordial one, 

 and from the end of that another, and so on to the amount of four or 

 five, before any lateral increase takes place. They then begin to in- 

 crease rapidly to the right and left, ultimately forming two roundish 

 lobes, with a deep intermediate sinus. As the cellules are added, 

 delicate fibrils issue here and there from their lower surfaces at or 

 or near their union with one another, taking a downward direction, 

 and finally insinuating themselves into the pores of the soil. The 

 lobes continue to increase externally until they have attained a cer- 

 tain size, when all external increase ceases : the primary frond is then 

 composed of a single lamina of cellules, which diminish in size from 

 the centre to the circumference, and in appearance very much 

 resemble the thallus or lobed frond of some Hepaticae. 



" But this is only one of the forms which the primary frond assumes. 

 Some increase more rapidly at first, and soon acquire a circular or 

 reniform shape, increasing by the addition of cellules at the circum- 

 ference ; others divide into a number of lobes, standing nearly upright; 

 while some produce one lobe after another, the lobes being recumbent, 

 one lapping over the other. Some again have both surfaces covered 

 with minute pedicellate glands ; while in others the glands are only 

 found on one side of the frond ; and some, as the different species of 

 Adiantum, are perfectly smooth and naked. 



" When the lobes have attained a certain size, external increase 

 ceases. A slight swelling may sometimes be perceived of the cellules 

 lying at the bottom of the sinus, and between the bases of the two 



