I 66 THE CACTACEAE. 



found more than 150 miles inland from the coast of the Gulf of California, and in southern Arizona 

 its range follows approximately the contour of 3,500 feet on the east and north, and the lower course 

 of the Colorado River on the west. It is found in California only in three restricted localities on the 

 Colorado River and reaches its northern limit on that stream at a point about 40 miles north of the 

 mouth of the Bill Williams Fork. 



"The occurrence of the sahuaro is by no means continuous throughout this area, for it is never 

 found in deep alluvial soil and is relatively rare on the nearly level plains in the drainages of the 

 Altar, Santa Cruz, and Gila rivers. It is extremely abundant on coarse detrital soils adjacent to 

 the larger and smaller mountains and is very common wherever there is rock in place, ascending the 

 mountains in diminishing numbers to an elevation of about 4,500 feet. The absence of the sahuaro 

 from alluvial soils is undoubtedly related to the adverse conditions of soil aeration in these areas, 

 and possibly to the lack of good mechanical support. 



"The localities in which the sahuaro reaches its greatest size and abundance are the uppermost 

 portions of the slopes adjacent to small mountain ranges and hills, particularly where there is a 

 southern or southwestern exposure. In localities of this sort throughout southwestern Arizona, 

 it reaches a height of 30 to 35 feet, which is very seldom exceeded. Individuals of this size are freely 

 branched and often have a gross weight of as much as 6 to 8 tons. In the vicinity of Tucson branch- 

 ing begins on attaining a height of about 15 feet, but on the edges of the range of this cactus branch- 

 ing individuals are relatively uncommon and the maximum size is rarely reached. 



"The flowers of the sahuaro are borne at the crown of the main trunk and the lateral branches, 

 usually appearing in May, while the fruit matures some weeks in advance of the summer rainy season. 

 The small seeds are borne in great profusion, but are eaten by birds and ants so rapidly that the 

 crop is seriously decimated before the requisite conditions for germination occur. The seeds 

 germinate readily at the high temperatures of the summer rainy season, but the growth of the seed- 

 lings is extremely slow, so that the end of the second year finds them only one-fourth of an inch in 

 height, and at an age of 8 to 10 years they are still less than 4 inches high. The growth continues to 

 be slow up to a height of 3 feet or more, so that individuals of that size are approximately 30 years 

 of age. After reaching this size the growth rate is rapidly accelerated until it reaches a maximum 

 of about 4 inches per year. The largest individuals are 150 to 200 years of age. 



"The sahuaro appears to suffer from very few diseases and natural enemies, the greatest 

 decimation in its numbers being occasioned by mechanical agencies. When struck by lightning 

 or wounded in any other manner during the dry season, it recovers very rapidly by the formation 

 of a heavy callus over the wounded spot. If it is wounded in the rainy season, however, bacterial 

 decay sets in very rapidly and a large plant may be destroyed in less than a week as a result of a 

 small wound. The nests made in them by woodpeckers are always lined by heavy callus and appear 

 to occasion no permanent injury. 



"The roots of the sahuaro are shallowly placed and widely extended, often reaching a distance 

 of 50 to 60 feet from the base of the plant. The woody tissue may be compared to a series of bamboo 

 fishing rods arranged parallel to each other in the form of a cylinder. These woody rods increase in 

 thickness with the age of the plant, so that they form a very substantial framework at the base while 

 they taper at the summit to slender elastic rods. The fleshy tissue is found both within and outside 

 the circle of the wood} 7 rods and the water content of these two regions appears to be the same. 

 Determinations made near the top of the plant indicate that there is 98 per cent of water on the 

 basis of the wet weight. There are great fluctuations in the water content of the tissue from season 

 to season and it has been shown that large quantities of water are taken up dur- 

 ing the rainy seasons, particularly in the summer, and that this water is gradually 

 lost during the dry seasons, particularly in May and June. The sahuaro, like 

 many other cacti, is able by reason of its external form to adjust its size to 

 these fluctuations in volume. 



"This plant is an extremely useful one to the aborigines of its natural range. 

 The heavy rods are used as construction material in building houses and enclos- 

 ures, and the fruit and seeds are used for making both food and drink by the 

 Papago and Pima Indians." 



Illustrations: Amer. Bot. 20:87; Journ. N. Y. Bot. Gard. 9:^32; 

 pi. 49 to 52; Nat. Geogr. Mag. 21 : 651 ; Safford, Ann. Rep. Smiths. Inst. 

 1908: f. 20; Shreve, Veg. Des. Mt. Range pi. 3 b, 4, 5 to 8; St. Nicholas 

 42: 366. Amer. Gard. n: 451, 528; Ann. Rep. Bur. Amer. Ethn. 26: pi. 

 8, f. b; pi. 9; Bull. Torr. Club 32: pi. 3, 4; Caet. Journ. 2: 84, 130; FlG - 

 Caet. Mex. Bound, pi. 61, 62; Curtis's Bot. Mag. 118: pi. 7222; Cycl. ^Tox,. g,ga "" 



