"The what?"

"Sage brush. The same taste will be in everything you eat out in this country--that and the alkali."

"Then I starve," announced Stacy, firmly, laying down his fork and folding his arms.

"Any time you starve it'll be because there is nothing to eat,"

retorted Ned.

"You'll all get used to the taste after you have been out a few days,"

comforted the guide.

"Never!" shouted Stacy.

"I rather like the peculiar taste," smiled Tad Butler.

"Good as a tonic," spoke up Walter.

Thus encouraged Stacy tried it again, at first nibbling gingerly at the bacon, then attacking it boldly. Even the Professor, after a time, appeared to forget the bitterness of the food, pa.s.sing his plate for more.

Tom Parry smiled indulgently.

"You'll all like it after a while," he nodded.

"I'm sure I'll have to take back some sage brush with me to flavor my food after we leave the desert," scoffed Ned.

Supper finished the dishes were cleared away, after which the party threw themselves down beside the camp-fire in keen enjoyment of the hour. The evening was delightfully cool, with not a trace of the baking heat of the day.

"Doesn't seem possible that there could be such a change in the temperature in so short a time," marveled the Professor.

"It is the mood of the desert," answered the guide.

"What time do we start in the morning?" interrupted Tad, approaching them at that moment.

"I was just about to suggest that we break camp at daylight, traveling until the sun gets hot. We can then pitch a tent or two during the middle of the day, and rest for a few hours."

"Why not keep on all day?" asked the lad.

"It would prove too great a strain--both on man and beast. At noon we will eat a cold lunch, as too much food in this heat is not good for us. You will find the temperature rising as you get further south, and the hardships increasing in proportion."

"We shall not fall by the wayside," laughed the boy.

"No; I am convinced of that. You lads are as tough as pine knots, but you will need all the endurance you have for this trip."

"If we are going to turn out so early, I think you boys had better go to bed pretty soon," advised the Professor.

"That's why I asked you, sir. I rather thought Mr. Parry would wish to make an early start in the morning. I'll see to the ponies; then I'll go to bed."

"Never mind the ponies. I'll look after them," answered Parry.

"That boy is a splendid type," he continued to the Professor, after Tad had walked away from them to notify his companions of the plans for the morrow.

"They all are," answered the Professor.

"Yes, I have been observing them all day. To tell the truth I was rather doubtful about the wisdom of taking a number of boys across the desert. It's bad enough for men well hardened to the work."

"I trust your apprehension no longer exists," smiled the Professor.

"Not a trace of it left," replied Parry, with a hearty laugh. "Young Brown handled that bucking pony splendidly this afternoon. He's a good horseman for a boy."

"Master Tad is a better one. You'll agree with me if you get an opportunity to see him in any work that's worth while."

"Well, good night, boys," called the Professor, as he saw the lads moving toward their tents.

"Good night, Professor, sleep tight," they shouted merrily altogether.

"Good night, Mr. Parry. We'll be up with the birds."

"Birds," sniffed Stacy. "A tough old hen couldn't live out on this desert."

In a short time the camp settled down to sleep. The guide, with a last look about and a long, comprehensive study of the sky, sought his own tent, where in a few moments he, too, was sound asleep.

After a time the moon came up, in the light of which the weather-beaten tents of the Pony Rider Boys were mere specks on the vast expanse of desert.

Not a sound disturbed the quiet scene. However, had any of the occupants of the little tents been awake, they might have observed a thin, fog-like film drifting across the sky from the southwest. On and on it came until finally it had blanketed the moon, casting a veil over the landscape.

Other sheets of film arose from out the southwest, placing layer after layer over the fast fading moon, until finally it was obliterated altogether.

The desert was working out another of its mysterious phases, but none in the camp of the Pony Riders were awake to observe it.

A dense pall of blackness now hovered over the southwest.

All at once a squirming streak of lightning wriggled along the horizon, like a golden serpent, losing itself by a downward plunge into the black abyss beyond the desert.

The air grew suddenly hot and depressing, while a gentle breeze stirred the sage brush on the higher places. The ponies moved restlessly in their sleep, kicking out a foot now and then, as if in protest at some disturbing presence.

Tad Butler, ever on the alert, roused himself, and stepping out in his pajamas took a survey of the heavens.

"I guess we're going to have a storm," he muttered. "I wonder if I ought to wake Mr. Parry? He thought, this afternoon, that there was a storm brewing. Still, there's nothing he can do. The tents are staked down as securely as is possible. No, I guess I'll go back to bed."

The lad did so, and after a few moments of wakefulness, dropped off into a sound sleep.

A few moments later the breeze increased, picking up little patches of sand, which it hurled into the air, scattering the particles over a wide area. Far down to the southwest a low roar might have been heard, and from the blackness there a funnel-shaped cloud detached itself, starting slantingly over the desert. It appeared to be following a northerly course, more or less irregularly, and from its direction, should pa.s.s some miles to the westward of the sleeping camp.

Whirling, diving, swooping here and there, lifting great patches of sand and hurling them far up into the clouds, the funnel swept on.

Suddenly, when about three miles to the southwest of the camp, it seemed to pause hesitatingly; and then, as if all at once having descried the little group of tents, started swaying, tottering toward them. As it moved the disturbing roar continued to increase in volume.

Tad Butler heard it now.

He slipped from his tent and stood listening apprehensively.