MICROSCOPIC OBJECTS. 41 



Fig. 81. Capsule of a Moss in the act of discharging its 

 Spores (Tortula subulata) , x 20. 



Mosses are divided into two great sections, called Acrocarpi 

 and Pleurocarpi, Acrocarpi signifying that the capsule borne 

 on the fruit-stalk or seta terminates the moss, and Pleuro- 

 carpi that the fruit-stalk springs from the side of the stem 

 of the moss. 



These groups are again divided, according to the structure 

 of the peristome, into Aploperistomi and Diploperistomi. 

 The drawing shows the single peristome (section Aploperi- 

 stomi) in the act of discharging the spores. It is drawn as 

 seen under the parabolic reflector. 



The genus Tortula has been so called from the spirally 

 twisted peristome, which will be 'seen in the drawing ; it is 

 the most common of all the genera of Mosses, and the species 

 are chiefly found on walls, very rarely on banks, trees, &c. 



The object may be mounted in balsam. 



Fig. 82. Capsule and Peristome of a Moss : opaque view 

 (Funaria hygrometrica) , x 20. 



The division Diploperistomi is represented by this drawing, 

 although a better view of the double peristome will be seen 

 in fig. 84. The seta of this Moss has the property of twisting 

 itself upon the application of water, from which property it 

 has gained the specific name of hygrometrica. It is one of 

 our commonest Mosses, being found on the top of nearly all 

 old walls &c. ; it is also very commonly found growing where 

 a fire has lately deposited wood-ashes. A longitudinal sec- 

 tion of the young green capsule of this Moss is a good subject 

 to show the position &c. of the columella (see fig. 83) . 



The ripe capsule, as shown in the drawing, is best mounted 

 in a dry opaque cell. 



