Seasonal differences.—As might be expected from the data presented under "climate," the conditions are fairly uniform. The general appearance of the islands is the same at all seasons of the year. Of course during the winter months and early spring, after the heavy rains in September to December, there is more green carpeting in dry places, due to various grasses and low herbs which turn brown and dry in the later and hotter summer months, and such tropical trees as the large Ficus hispida, planted in the courtyard at the light-house on Loggerhead Key, drop their leaves during the coolest months, Decem ber and January. But this dormant condition lasts only a few weeks; other plants, as the Hibiscus and oleanders, seem to bloom and flourish throughout the year, and during the summer months particularly are covered with showy crimson, scarlet, and pink blossoms.
Flowering and fruiting.—These phenomena are not definitely limited in the Tortugas region. Coconuts frequently bloom and ripen at the same period, and the same is true of the geiger-trees, some of which have showy clusters of scarlet flowers and bear on the same branch the hard, pointed, white fruits. The Sccevola often bears its white blossoms simultaneously with the large edible-looking but nauseating black berries. Some periodicity, however, has been noted in the red man grove and the sea-grape, Cocolobis uvifera. Trees were seen with blossoms and ripe or nearly ripe fruits, but never trees with blossoms together with very immature or half-ripe fruits and fully ripened ones. There must be some definite cycle of growth which prevents the occur rence of fruits at all stages in these trees.
Suriana seem to have cycles of growth not separated by long periods, for some individuals are frequently seen having flowers and ripe seeds. The Convolvulacete, represented by Ipointea and Calonyction, appear to have all stages of flowers and fruits, for even long periods of drought do not seem to prevent Ipoincea pea-wpm from producing its showy rose-purple funnels along the runners trailing 20 to 30 feet across the burning white sand-beaches.
Influence of soil.—There is not much field for observation under this head, since the islands are essentially all alike geologically—i. e., the soil is all white calcareous sand, but at several places in the Tortugas there is a slight variation in the soil. On Bush Key, near the small tidal pool, the soil is lower than the adjacent sand and various unicellu lar and a few filamentous algae (e. g., Ifyngbya), etc., grow among the mangrove seedlings. In similar situations on Boca Grande the writer observed Sesuvium, Alternanthera, and Baas maritima in salt meadows or marshes where young rhizophoras were also establishing themselves. However, on Bush Key only an algal flora was observed on the surface of the soil and on the mangrove stems.
The other variations in soil were due to artificial conditions. On Loggerhead several carloads of soil had been brought from Maple wood, New Jersey, and this supports a few introduced weeds, such as Syntherisma and Cenchrus echinatus, with several Poinsettias. On Garden Key portions of the parade-ground, possibly through long years of cultivation and some attempts at fertilization and artificial watering, show a difference in the soil from that of the rest of the key. The accumulation of some humus here also makes a change in the soil's character. This portion of the parade-ground is thickly covered with a mat of Lippia, various examples of Sida, Dolicholus, etc. plants which need slightly more nutriment in their substratum than is etc., by the coarse, limy gravel and sand of other parts of the key.