264 



BOTANY OF CROP PLANTS 



brac\eo\e 



bility that the soil is more quickly exhausted by seeded 

 hops than by seedless ones. 



The Mature Fruit. — The fruit (Fig. 105) is a small achene 

 surrounded by the persistent cup-shaped perianth. The 

 single seed within has a curved 

 embryo about which is a small 

 amount of endosperm. 



Lupulin Glands. — In the ma- 

 ture hop, the outer surface of 

 the bracteoles, the perianth, 

 and, to a less extent, the bases 

 of the bract-Hke stipules are 

 covered with yellow pollen-like 

 grains, the so-called " hop-meal " 

 or "lupuHn" (Fig. 105). 



Each yellow grain is a cup- 

 shaped, multicellular, glandular 

 hair filled with a resinous secre- 

 tion. It is an outgrowth of an 

 epidermal cell and consists of a 

 short stalk and a cup of one 

 layer of cells. Each cell has a 

 rather thick cuticle. The secre- 

 tion of the cells collects just 

 beneath the cuticle, raising the 

 latter up until finally the cup-shaped depression is filled 

 with the secretion which remains covered by the cuticle itself. 

 In immature hops, the lupulin glands are bright yellow and 

 transparent. In mature hops, they are a paler yellow and 

 somewhat opaque. The commercial value of hops depends 

 entirely upon the amount and quality of the "hop-meal." 

 It constitutes from 15 to 32 per cent, by weight of the hop. 

 Geographical. — The hop grows wild in England, the 



Fig. 105. — Hop (Humulus lupu- 

 lus). A, bracteole; B, immature 

 lupulin gland; C, same in section; 

 D, mature lupulin gland; E, same 

 in section. (B-E after Percival.) 



