20 STUDY OF NUTS MICROSCOPIC IDENTIFICATION. 



edly heart-shaped, while the third is elongated, roughened, and very 

 similar in size and appearance to the native /. cinerea. Whether 

 these forms are to be ranked as distinct species is a question not 

 entirely settled, as it is certain that they display a marked tendency 

 to fail to come true from seed, and it is the common opinion that 

 seedlings grown from nuts of any of the three types may produce 

 nuts of the other types or of intermediate character. In vegetative 

 characters, moreover, these three forms appear to be practically 

 identical, this fact being explained in either of the following ways: 

 (1) That they are three separate but ill-defined and variable species, 

 distinct enough in their extreme forms, but connected by intermediate 

 stages and overlapping in their variations, possibly as a result of 

 intercrossing; (2) that there is but a single exceedingly unstable 

 species, possibly in a state of mutation, the original form giving rise 

 mainly to two types. Since the form known as /. sieboldiana pro- 

 duces the finest nuts, it is the one here described (fig. 5, A). 



A B 



FIG. 5. A Japanese walnut (natural size) ; B California black walnut (natural size). 



The Japanese walnuts are usually smaller than are the nuts of 

 either /. regia or J . nigra, while the surface features of the shell are 

 intermediate between the two species. The shells are moderately 

 thick, the kernels smooth, plump, of good quality, and relished by 

 most people. The tree is hardy and productive, and although these 

 nuts do not offer as great promise as do the native species, they should 

 be included in home plantings wherever successful. A small sample 

 examined by the writer contained 26.92 per cent of kernels. 



Histology. The outer layer of the periderm resembles closely that 

 of the Persian walnut, but the cells are slightly more angular, and 

 hence the foamlike appearance is less marked (fig. 6, A). The 

 stomata, however, are peculiar. The guard cells are nearly always 

 coiled into complete circles with the ends meeting or, in some cases, 

 even overlapping. The length is, therefore, much less than the width, 

 these dimensions being usually 40 to 50 jx and 60 to 80 JJL, respectively. 

 They are much more numerous than in the Persian walnut. In the 



