Your theory of vegetation becomes more and more probable.

Schiaparelli in a letter to Lowell.

Let one stand on some peak of the Verd Mountains, northeast from Phoenix, Arizona, overlooking the Gila River as it follows its course across the desert, and after the river is lost to view he will notice that the foliage along its banks marks its course. If one takes this view in winter time, the uniform gray of the plains, unbroken by a single shade of color blends with the light blue of the distant Plomas and Castle Dome Mountains on the southwest horizon. In the early spring when the water is first let into the irrigating channels with their innumerable divergent ditches, a shade of green may be seen emerging from the monotonous yellow-gray of the hot and sterile plain, first conspicuous near the source of the water supply, and then following along to Phoenix, Tempe, and other regions till in full efflorescence these cities stand out like great green carpets spread upon the Earth. From this mountain top not a trace of an irrigating ditch, large or small, would be discerned, except here and there a glint of reflected sunlight, but the effects of the life-giving waters can be traced in broad bands to the remotest limits of the water channels, when they would end as abruptly as they had begun.

If we examine railroad maps, the lines of which represent the road-beds utilized to convey passengers and freight to various places, we shall observe that in mountainous regions the lines run very irregularly, often paralleling mountain chains, or following rivers. On level areas such as Iowa, Texas, and other states, the railroads run for hundreds of miles in straight lines, at times converging towards large centres of population. Their occasional parallelism and radiation from centres, all present a certain cachet in angles of approach and alignment that reminds one strongly of similar features in the markings of Mars. If each railroad were bordered by a wide growth of trees with sterile desert between, these broad bands as seen from Mars would be identical with the appearance of similar lines in Mars as seen from the Earth. In Mars, however, there are no high elevations since the terminator of Mars stands out clear cut and not jagged as in the Moon. The planet being devoid of hill ranges, and large oceans, the canals can run in straight lines for hundreds of miles. If it were possible to conceive by analogy a creature on Mars furnished with a telescope, he would undoubtedly correlate the irrigating regions of Arizona as similar in nature to his own canals. The irregularity of the rivers running through such regions would puzzle him quite as much as we are puzzled by the absolute straightness of the Martian canals. He would, of course, observe that in our winter the irrigating areas became invisible, to appear again as our summer advanced. His own experience of vegetation arising from irrigation alone and starting from the north when the first water from the melting snow cap animated the growth of plant life, and proceeding slowly towards the equator would prevent him from understanding the reverse condition on our planet, with the shade of green being perennial at the equator and spreading slowly north with the advance of summer.

The marvels of irrigation are impossible to conceive of without first seeing a parched land before the water channels are dug and the exuberant vegetation springing with the water's advent. The illimitable stretches of arid plain, no green, rarely an evidence of life, and then usually in hideous shapes like the hissing and purple-mouthed Gila monster; hot pale dust; blinding sunlight; ragged clumps of gray sagebrush, rebuking by their hopeless color and dishevelled appearance, the intolerable condition of their existence; angular cacti, surviving because of their vicious needles, and then literally a step only from this sterile waste, and one finds himself wading through rich, soft alfalfa, under the deep shade of cottonwood trees, glistening threads of water when the overhanging vegetation does not hide the channels, brilliant flowers, singing birds, fat cattle and vociferous children.

In this apparently irreclaimable desert of Arizona, have sprung up prosperous cities, great farms and fruit orchards. About Phoenix, more than one hundred and twenty-five thousand acres are under the richest and most profitable cultivation, and all due to a little narrow canal which conveys the water from Salado River, and distributes it by narrow ditches, so narrow, indeed, as to be invisible except on the nearest approach. There have already been constructed in the Gila Valley alone, two hundred and fifty miles of ditches, and four hundred miles of parallels. Mr. Ray Stannard Baker, in the "Century" for July, 1902, presents in a graphic way, the marvels of irrigation. Major J.W. Powell, during the later years of his life devoted his whole time and energy to urging the reclamation of desert lands in the West by irrigation. In his reports on the subject he estimated that a region equal in size to New England, New York, Pennsylvania, and West Virginia could be recovered from the desert sands of Arizona and other regions in the West. In India, millions of pounds have been spent for irrigating canals and ditches. A single canal with its tributaries drawing water from the Ganges measures 3,910 miles in length, bringing into cultivation one million acres of land at an expense of fifteen millions of dollars. The idea of irrigation is not due to the advanced intellect of man; it has been the result of dire necessity and is of great antiquity. Mr. Frank Hamilton Cushing discovered evidences of the most extensive irrigating canals among the ancient Pueblo Indians of Arizona.

Sir C. Scott Moncrief, in his address as president of the engineering section of the British Association for the Advancement of Science, describes the various forms of irrigation. The primitive method consists in raising water by human labor. Early Egyptian sculpture depicts laborers raising water by means of buckets, and along the banks of the Nile the same method may be seen to-day. Other methods of raising water are by pumps driven by windmills. In certain regions Artesian wells furnish water for irrigation. The importance of irrigation is best shown in the fact, that, while the rainfall in Cairo is, on an average, one and four tenths inches a year, yet in the immediate neighborhood land brings $750 per acre; this value being due to irrigation alone. In speaking of water storage for supplying the irrigating canals the author says: "When there is no moderating lake, a river fed by a glacier has a precious source of supply. The hotter the weather the more rapidly will the ice melt, and this is just when irrigation is most wanted." (Judging from this dictum, the condition in Mars is ideal.) In speaking of the great Assouan Reservoir in Egypt, he says: "The sale value of land irrigated by its waters will be increased by about $125,000,000. The increase in irrigation areas in our Western States may be appreciated by the following figures. In 1889 it amounted to 3,564,416 acres; in 1900, to 7,539,545 acres. Now it is at least 10,000,000 acres. Without irrigation this land sold for four or five dollars per acre; with irrigation it brings forty dollars per acre.