20 ACADEMIC BOTANY. 



36, In the lowest geological formations (see Lesson XIII.) the rocks 

 are without organic remains ; ahove these, fossil Seaweeds appear ; a 

 little higher, Ferns and Pines; then Cycads and Palms; then the Oak, 

 Maple, Magnolia; then the thousands of grasses, herhs, shrubs, and 

 trees. It is of the profoundest interest to the student to see how, 

 through slow periods of time, plants of the higher types were brought 

 forth ; and how, as the earth became better fitted for man, the ancient 

 growths were supplanted by these higher types, leaving only here and 

 there some microscopic descendant, like the lied Snow and the Dia- 

 tom, or some solitary patriarch, like the Dead-Man 's-Eope, the Tree 

 Fern, Pine, and Palm, to tell the story of that strange elder time, 

 which did its work and passed away ages before man appeared on the 

 scene. 



On a stone exposed to moist air and shaded from the sun, or on one 

 over which water flows continually, we And delicate blotches, usually 

 green, sometimes olive, brown, or red. These are composed of myriads 

 of tiny plants. Seaweeds, Moulds, Fungi, Lichens, etc. They live their 

 little life of a day, an hour, a week, a year. They die, and their remains 

 form a nidus, or nest, for the mosses. Minute phanerogams (grasses, 

 etc.) succeed the mosses ; the stone is not only covered, but gradually 

 pulverized ; soil is formed. This soil is suited to the growth of shrubs 

 and trees, and the once bare granite thus becomes fertile earth, ready 

 for the abode and sustenance of man. We see this miracle daily, the 

 same now as in the beginning. It shows us that creation is a con- 

 tinued energy, not an accomplished work. Nature has a forward as 

 well as a backward look ; the stones and plants, her eloquent prophets, 

 not only unveil the past, but predict the future. Bach stone holds the 

 imperishable history of its own organisms ; each organism foreshadows 

 the type that is to succeed it. 



37. One-celled plants. The Cell defined. — Among the 

 AlgcB — usually called Seaweeds, though many of them are 

 fresh-water plants and some of them land plants — we find 

 the simplest expression of organic life. We see the green 

 blotches on the stone ; the crimson patches on the north 

 side of a damp cliff; the Blood-rain that falls in different 

 parts of the world ; the delicate stuff called Red Snow (Fig. 

 11, D) which appears so often on the true snow in the Alps, 

 the Pyrenees, and in British America, where it covers the 

 rocks on Baffin's Bay to a depth of ten feet. These consist 

 of myriads of individual plants, each plant being a single 

 cell. Their color is due to 



A. Chlorophyl, or leaf-green (Gr. chloros, green, phyllon, 

 leaf), the substance which gives verdure to leaves. We 

 examine one of these little plants under the microscope (Fig. 

 11, D). It is a simple cell or globe, with a closed outer 

 wall of soft elastic material called 



