CALAMITES AND LYCOPODS 371 



sterile and fertile branches that will appear the following 

 spring. We thus have an excellent illustration of the division 

 of physiological labor one branch to anchor the plant in 

 the soil, and serve as a storehouse of food and a center of 

 distribution; roots to take in water and dissolved minerals; 

 sterile aerial branches to perform the functions of food- 

 manufacture, and the fertile branches to perform the func- 

 tion of reproduction bearing the spores, and lifting them 

 high in the air, thus facilitating their distribution by wind. 



The fertile branch commonly appears first in the spring, 

 usually bearing no side branches nor foliage-leaves, but 

 only whorls of scale-like leaves at each node. These 

 scales possess little or no power of photosynthesis, and 

 are chiefly protective (Fig. 267). In some instances the 

 fertile branches bear green lateral branches. At the 

 apex of the fertile branch is borne the strobilus, or cone, 

 consisting of a central axis (the prolongation of the 

 axis of the branch), bearing a variable number of spor- 

 angiophores. In the development of the fertile branch the 

 cone is formed first, and is raised above ground by the 

 subsequent formation and elongation of the sterile tissue 

 below it. In some species (E. arvense) the fertile branch 

 dies after the shedding of the spores, while in other species 

 (e.g., E. pratense), after the spores are shed the entire cone 

 falls away and the fertile branch then takes on the char- 

 acters of the sterile branches which occur with it. 



Each sporangiophore 1 consists of a stalk with a peltate 

 shield at the end The axis of x the cone soon ceases to 



1 The sporangiophores of Equisetum have been interpreted as hom- 

 ologous with leaves, i.e., as sporophylls, but evidence derived in part from 

 a study of the fossil relatives of the modern horsetails indicates that this 

 conclusion may not be correct (Cf. Fig. 268). The term sporangiophore 

 isnon-commital as to homology. 



