26o BOTANY OF CROP PLANTS 



trorse hairs on each of the six edges of the stems, and on the 

 petioles and leaf veins. The main stems bear opposite 

 lateral branches. These reach their greatest length near the 

 middle of the main stem. They bear the pistillate inflores- 

 cences (hops), and hence it is important that they be formed 

 in abundance. 



Leaves. — The hop leaves are opposite, broad, palmately 

 veined, and three- to five-toothed (Fig. 103). In palmately 

 veined leaves there are several main veins which radiate 

 from the leaf base. The stipules are broad, those of opposite 

 leaves being united. 



Inflorescences. — Hops are commonly dioecious, rarely 

 monoecious. Hermaphroditism in hops has been noted. 

 Some have held that injury is the cause of this abnormality. 

 This theory has been refuted by Stockberger as a result of a 

 number of experiments in which the plants were cut back, 

 or pruned, or the tap root removed or portions of the crown 

 removed. All of them failed to develop the abnormality 

 (hermaphroditism) . Hop plants of this type arise independ- 

 ently of injury. They transmit the abnormality to their 

 progeny when propagated vegetatively. It is held that 

 perfect flowers appear only in pistillate inflorescences. 



Staminate inflorescences (Fig. 103, B) are paniculate, and 

 grow from the axils of the main shoot or from the axils of 

 lateral ones. Pistillate inflorescences (Fig. 103, A) are spike- 

 like in appearance. They are the "hops" of commerce and 

 are often spoken of as "burrs" or "strobiles." These are 

 mostly borne on lateral branches from the main stem; they 

 arise in the axils of the leaves. 



The pistillate inflorescence has a central, hairy axis (Fig. 

 103, C) upon which are arranged a number of very short 

 lateral branches or axes. At the base of each short lateral 

 branch, or axis, is a pair of bract-like structures. These are in 



