EXPLANATION OF THE PLATES. 



c. Nut within ditto, the end to which the stigmata were attached placed down- 

 wards: p. 91. 



d. Inferior part of the nut c ; p. 91. 

 €. Superior of ditto : p. 91. 



f. Stem and branches of recent C. hispida. 



g. Ditto magnified. 



h. Section of the stem ; the smaller tubes are irregular in number : see p. 91. 



Fig. 3. a. Pericarpium of recent Chara vulgaris ; from the Bakie Loch. The stems 

 only of this species have been found fossilized in the rock-marl : p. 93. 



b. Ditto, magnified 20 diameters : p. 93. 



c. Nut within the integument 6, the end to which the stigmata were attached 

 placed downwards : p. 93. 



d. End of the nut c, to which the stem was attached : p. 93. 



e. End of ditto, to which the stigmata were attached. 



f. Stem and branch of C. vulgaris, natural size. 



g. Stem and branches of ditto magnified 8 diameters. 



Fig. 4. a. Pericarpium of a species of Chara found in many of the marl-lakes of For- 

 farshire, but not in the Bakie (p. 93.), the C. flexilis of Dr. Hooker's Flora 

 Scotica. 



b. Ditto magnified, and attached to the branch. The spiral valves of the integu- 

 ment turn each about 2^ times round the circumference, the whole forming about 

 13 rings, which exceed the number in C. hispida and vulgaris, p. 93 : the septa 

 mentioned p. 91, are seen through the transparent stem. 



c. Nut within ditto. 



d. Branch of C. flexilis, natural size. 



Fig. 5. represents a species of Helicteres, from the West Indies, of the natural size ; 

 — introduced as a subject of comparison, with the integument and nut of the peri- 

 carpium of Chara : p. 91. 



Plate XIII. 



Fig. 1. Chara Medicaginula, magnified 20 diameters, from the lower freshwater 

 formation at Gurnet-bay in the Isle of Wight. 



Fig. 2. a. The same, natural size. 



b. Section of the same, magnified 20 diameters, exhibiting the nut inclosed within 

 the integument. 



c. Part of one of the spiral valves, magnified. 



Figs, 3, 4, 5. Chara Medicaginula from the Isle of Wight, magnified 20 diameters. 

 In these three specimens the number of the ribs or striae on the nut varies from 

 5 to 7. Whether they should in consequence be referred to three distinct spe- 

 cies, the present state of botanical knowledge concerning the fructification of this 

 tribe of plants is not sufficiently advanced to determine. The nut in figs. 3 and 4 

 is perhaps partially, and that in Jig. 5 much distorted : p. 93. 



Fig. 6. Stem of Chara Medicaginula, found accompanying the preceding. It is strictly 

 analogous to the stem of C. hispida : see PI. XII. 



