THE FERNS AND THEIR ALLIES 7 



plant, that is, the assimilating of carbon from 

 the carbonic acid of the atmosphere. The real 

 leaves of the Horsetail are much reduced in size, 

 and take very little part in the work of nutrition. 

 We shall find them at the joints of the stem as 

 rings, each collection forming a kind of sheath. 

 The leaves, which are usually of the same 

 number as the branches, show no sign of their 

 individuality, save in the little projecting teeth. 

 In some species the fertile shoots, which appear 

 in the form of cones, are produced specially. 

 These appear in the spring before the ordinary 

 vegetative growths, and are quite destitute of 

 chlorophyll. In other species the normal 



reen shoots are fertile at the termination, 

 he sporangia are borne on curious scale-like 

 leaves, a large number of which go to the 

 making of a cone. 



One or two aquatic plants, which belong to 

 the Vascular Cryptogams, call for comment. 

 The Pillwort is a singular plant not uncommon 

 in damp situations. The leaves of this plant are 

 narrow, and the spores are produced in curious 

 rounded processes. The Water Fern (Azolla) 

 is an introduced plant which sometimes grows 

 abundantly on lakes in the South of England. 

 Both the before-mentioned plants are allied to 

 the Ferns. The Water Club Mosses (Isoetes) 

 are represented in this country by a species 

 commonly known as the Quillwort. This 

 plant grows in lakes, and is easily recognized 

 by its quill-like foliage. 



Owing to the large number of species a some- 

 what elaborate classification is necessary in the 

 case of Ferns. In distinguishing the different 

 families, the manner in which the collections of 

 spore cases, known as sori, occur, as well as the 

 features which the individual sporangia present, 



