98 THE PLANT WORLD. 



mond saw, and the slices ground down as above described. In fact 

 the whole object may be sliced up serially, just as fresh objects are 

 cut with a microtome, although of course with more loss. 



The accompanying plate shows sections cut from a piece of fossil 

 coniferous wood found in the lower Cretaceous near Washineton, D. 

 C. It is known as Ciipressinoxylon McGeei^ and is thought to repre- 

 sent the wood of Sequoia, of which nearly fifty species have been 

 found fossil. Figure i is a transverse section through a ring of 

 growth, a in the figure representing the layer of fall wood and b the 

 spring wood. The letters c and d refer to intercellular spaces. Fig- 

 ure 2 is a tangential section of the same, showing at a a. resin-duct 

 made up of short-cells; d, pits on the wood-cells, and c the sections of 

 pits on the other or radial walls of the wood-cells. Figure 5 is a sec- 

 tion in the same direction as that in figure 2, but a different trunk of 

 wood. Figure 3 is a radial section highly magnified, showing the 

 wood-cells with the large circular pits, d, and the medullary ray with 

 oval pits at a. Figure 4 is an enlarged transverse section showing 

 cells of spring wood. Figures i, 2 and 5 are enlarged 67 diameters, 

 and figures 3 and 4 are enlarged 242 diameters. 



The use of this plate is by the kindness of the U. S. Geological 

 Survey. 



TUNA AND ITS USES.* 



L>y Walter Hough. 



ONE of the most useful plants of Mexico is the tiuia {Opuntia 

 tuna), great numbers of which occupy the waste lands of the 

 country. From time immemorial the people of Mexico have 

 prized the so-called "figs" of the tuna, which are of many 

 sizes and colors and form an important article of food among all 

 classes. The fields of nature's own planting furnish them freely and 

 in abundance, and the season of their ripening is a happy one for both 

 man and beast. At this time half the population retire from their 

 houses and camp in the country, engaged in the pleasant and remunera- 

 tive occupation of preserving the fruit. 



The tuna figs of the southwest United States are also prized by 

 the Indians, but the fruit is rarely larger than a gage plum, while in 

 Mexico it attains the regal size of a Bartlett pear. 



Tunas look easy to the unwary visitor from another clime, and 

 there are few who have not gathered them in haste to repent later, for 

 the tufts of bristles that beset the fruit yield the palm to no other 



*The writer is indebted to Dr. Edward Palmer for the greater part of the information con- 

 tained in this article. 



