334 NOTES OF A BOTANIST 



of herbs exist there, which, burying themselves deep in the earth, 

 survive through the long periods of drought to which they are 

 subjected. Some of the smaller medanos, especially those under 

 the lee of a low ridge of land, may be seen to be capped with 

 snowy white, contrasting with the yellowish or greyish white 

 which is the ordinary colour of the sand, and yet at a short 

 distance liable to be taken for sand a little whiter than common. 

 The whiteness, however, is that of the innumerable short cylin- 

 drical spikes of an Amarantacea, whose stems, originating from 

 beneath the medano, ramify through it, and go on growing so as 

 to maintain their heads always above the mass of sand, whose 

 unceasing accumulation at once supports and threatens to over- 

 whelm them. 



The other two herbs of the desert are known to the natives, 

 the one as Yuca del monte or Wild Yuca, the other as Yuca de 

 caballo or Horse Yuca, from their having roots like those of the 

 cultivated yuca (Manihot Aypi\ or not unlike parsnips, but three 

 times as large. Both roots are edible, and the former is some- 

 times brought to market at Piura when the common yuca is 

 scarce. The Yuca de caballo is too watery to be cooked, but is 

 sometimes chewed to allay thirst by the muleteers and cowherds, 

 who detect its presence by the slightest remnant of the dried 

 stump of a stem ; for both kinds maintain a purely subterranean 

 existence during many successive years, and only produce leafy 

 stems in those rare seasons when sufficient rain falls to penetrate 

 to the roots. A few animals that roam over the desert, such as 

 goats, asses, and horses, obtain a scanty supply of food and drink 

 from these yuca roots, which they scrape out with their hoofs. 

 The fruit of the Yuca de caballo may freemen tly be seen blowing 

 about the desert, looking more like a pair of very long hooked 

 bird's claws than anything vegetable. It is an elongated capsule 

 with a fleshy pericarp (incorrectly described as a drupe), termin- 

 ating in a beak several inches long, and when ripe splitting into 

 two valves, which remain united at the base and curl up so as to 

 resemble claws or ram's horns. At Piura it is known by the not 

 very apposite name of espuelas or spurs. In Mexico the fruit 

 of an allied species is called Una del diablo or Devil's Claws. 

 The Yuca de caballo is a Martynia, of the family of Gesnerere 

 (or, according to some, of Cyrtandracere). I was fortunate 

 enough to see a single plant of it with leaves and flowers in 1863, 

 near the river Piura, on ground which the inundation had barely 

 reached, but had sufficed to cause the root to shoot forth its 

 stems, which spread on the ground, branching dichotomously, to 

 the distance of a yard on all sides. The roundish leaves, clad 

 with viscid down, are lobed much in the same way as those of 

 some gourds, but the large sweet-smelling flowers are like those 

 of a foxglove. 



