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EOSE — MEXICAN AJSTD CENTRAL AMERICAN PLANTS. 



83 



Purpus, as a guide, about twentj" species were studied. Here on the 

 diy white chalky plain are found many strikint( forms. One of the 

 most interesting' of these is Mamillarla anyalarls Link & Otto, form- 

 ing great clumps consisting of many individuals (PI. XYI). Here is 

 also found a giant Echinocactus (7^', ingens?)^ tlic flesh of which is 

 ujuch emploj^ed in making a highly prized confection. The plant 

 grows to l)e sometimes as nuich as 2.-1 nu'ters tall with a diameter of 90 

 to 120 cm. The body is cnt into sections resend)ling American cheeses 

 about 60 cm. in diameter and 15 to 20 cm* thick, and these are sent to the 

 candy factory where they are boiled with sugar and made into a candy 

 or ''dulce'' somewhat resembling preserved citron (PI. XVIT). In 

 the same region Opanthtimhricatii^ 0. tanicata{V\. -XVII), 0, Ideinae^ 

 and other Opuntias were abundant, and here we found a natural hybrid 

 between Opantia microdasys and another Opuiitia which has not been 

 spccificall}^ identified. Both species were growing near the hybrid. 

 While 0. micTodasyH is a low, pubescent, spineless species, the other 

 parent is tall, glabrous, and spiny, and the hybrid is somewhat inter- 

 mediate in size and without pubescence or spines. So far as my 

 observation goes natural hj^brids arc not common among the Cacta- 



ceae. 



Another very interestinij cactus desert which we visited is situated 

 around Tehuacan. It is remarkable (^specially for the great display of 



tree species belonging to Cercus, IMlocereus, Cephalocereus, anc 



d 



Opuntia. The cactus species of all genera seen here numbered 22. 



Two species of Echinocactus (/'/. f ave.H€eif}j< ^ E. rohmtus (PI. XVI)) 

 form great clumps, very nuich largi^r than any I had e\x*r seen before. 

 h\ the case of E. rohistiLs it was not uncommon to see masses 1 to 1.3 

 meters high and 3 meters in diameter, and in one example nearly 6 

 meters in diameter. These masses must have contained hundreds, if 

 not thousands, of individuals. A photograph of E. rohiistus is here 

 reproduced. 



On the hills east of th(^ town are great forests of the huge Gei>halo- 

 cereus macrocepl tal a^ (PI. XLIII, facing p. 12(>), which in many respects 

 resembles the much better known CepJialoccreus scnUis. Unlike the 

 latter, however, it develops a very woody trunk. Another striking 

 s])ecies is IHlocereuH falvicepH {V\. XVIII), which has a short, stout, 

 woody trunk and hundreds of nearly erect branches reaching a height 

 of 12 to 15 meters. Th(^sc branches set verv close toiretht^r and form 



«-V 



a cylindrical mass, not infreipiently 5 meters in diameter. 



P. 



s 



to the height of 2 to 3 meters, 

 is a common plant, while Cereus /lol/iarn/s' (PL XIX) is so common as to 

 be used as a hedge plant. Its fruit is as large as a goose egg. Another 

 Cereus near <7. ^iellaian (PL XX) is very common and furnishes fruit 



for the market. Escontrla ehiotUla (PL XLIIT facinerr). 12G)^ is still 



« See p. 126. 



