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 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 
is non-commital as to homology. 
