I30 



THE STRUCTURE OF ECONOMIC PLANTS 



cells. The guard cells of the stomatal apparatus are dumb-bell 

 shaped, and each one is paired with a triangular accessory cell; 

 Campbell (3) has described the development of the stomata in 

 maize. A vertical w^all is formed across the end of an epidermal 

 cell in the stomatal zone, cutting off a daughter cell w^hich is very 

 short. (Fig. 53.) This mother cell lengthens rapidly until it is 

 approximately square in surface outline, and, while it is develop- 

 ing, two small cells at the sides are cut out from laterally adjacent 

 epidermal cells. The accessory cells at first barely keep pace with 

 the growth of the mother cell; but, finally, grow much more 



Fig. 53. The development of stoma showing successive stages: ac c, accessory cells; g c, 

 guard cells ; m c, mother cell ; sto, stoma. (After Campbell, American Naturalist.') 



rapidly and in so doing modify the shape of the guard cells. The 

 mother cell rounds up and divides longitudinally, forming the 

 two guard cells; and, as these lengthen, the accessory cells begin 

 to grow more rapidly and become sub-triangular. The guard cells 

 continue to elongate until they are rectangular and two or three 

 times as long as broad. Meanwhile, the stomatal aperture which 

 is formed schizogenously between the opposing faces of the guard 

 cells elongates, the guard cells attain their final shape, and the 

 accessory cells become larger and more triangular. 



The Staminate Inflorescence. — The staminate inflorescence is 

 a broad panicle consisting of a central rachis, which is a continu- 

 ation of the central axis of the stem, and its lateral branches. 

 (Fig. 54.) The central rachis bears several rows of paired spike- 

 lets, while the lateral branches have only two rows of paired spike- 



