WALNUT. 23 



thickness in which it is difficult to distinguish cell outlines. Thick- 

 ened vascular areas occur at intervals. 



The endosperm is a single layer of cells, some of which may be 

 divided transversely, 40 to 50 [t. thick and united closely with the 

 embryo. The latter consists of roundish cells about 50 \i in diameter. 

 The embryo is rich in aleurone grains, which average about 10 \L in 

 diameter, occasionally reaching 15 pi. 



In /. calif ornica the epidermal cells of the integument are angular 

 and more nearly isodiametric than in /. hindsii. They are also much 

 smaller, having an average diameter of about 20 \L. Stomata are 

 numerous; they are about 45 pt, long and 52 \k broad, with very broad 

 guard cells inclosing a relatively small and narrow opening. There 

 is no suggestion of the coiling of the guard cells so noticeable in 

 J. hindsii. The seed coat is about 35 p. thick, and the aleurone layer, 

 which consists of about two cell layers, has a thickness of about 50 JJL. 



HICKORY NUT. 

 (Hicoria, Family Jiifflandacew.) 



The most striking difference between the walnuts and the hickory 

 nuts is in the character of the outer pericarp or husk, which, in the 

 latter, splits at maturity into four valves of a dry, leathery texture, 

 permitting the escape of the smooth, often more or less angular nuts. 

 Of the dozen species native within the United States, with few excep- 

 tions all but three produce nuts of too poor quality or bitter taste to 

 be useful as food. The shellbark, or king nut, H. laciniosa (Michx. /.) 

 Sarg., is less common in the market than either of the other species, 

 and as material for study was not readily available it is not considered 

 in this paper. 



PECAN. 



(Hicoria pecan (Marsh.) Britt.) 



From a commercial standpoint the pecan is by far the most impor- 

 tant of native nuts. Its smooth shell, attractive appearance, abundant 

 production, plump kernels, which are usually extracted with ease, 

 and high quality are largely accountable for its popularity. The 

 nuts are of various types, ranging from oblong cylindrical to almost 

 spherical. Those used in these studies were elongated, somewhat 

 pointed, of a grayish-brown color, and frequently splashed with dark- 

 colored markings. The husk of the pecan varies greatly in thickness 

 and does not always split entirely to the base until after the nut has 

 matured and fallen normally. Seedling pecan trees present a wide 

 variation in size and shape of nuts and thickness of shells. Propaga- 

 tion from the best of these seedlings has resulted in the production of 



