=UDOTEACEÆ= ^Penicillus^ ^P. dumentosus^ ^P. capitatus^ ^P. Phœnix^ ^Udotea^ ^U. flabellata^ ^U. conglutinata^ ^Halimeda^ ^H. tuna^ ^H. tridens^ ^H. opuntia^ =CODIACEÆ= ^Bryopsis^ ^B. plumosa^ ^Codium^ ^C. tomentosum^ =CAULERPACEÆ= ^Caulerpa^ ^C. prolifera^ ^C. Mexicana^ ^C. plumosa^ ^C. Wurdemanii^ [pg052] GRASS-GREEN SEAWEEDS "There can hardly be a more fascinating group of plants than this, whether to the strictly scientific botanist or to the more catholic lover of nature. The green algæ are among the most widely diffused of plant forms. They grow practically in every place where enough moisture, together with light and air, is to be had. Between tide-marks on almost every coast, floating on the surface of the deep sea, covering damp earth, walls, palings, and tree-trunks, sticking to the surface of leaves in the moist atmosphere of tropical forests and jungles, and inhabiting almost every river, brook, pond, ditch, or casual pool of rain-water in all quarters of the globe, are members of this ubiquitous group to be found."[3] [Footnote 3: Kerner.] The grass-green seaweeds are more simple in structure, and therefore are lower in order, than the red or brown algæ. They are among the lowest of all plants, many of them being minute single cells. They abound in fresh as well as in salt water, and in this respect differ from the other groups, the red and the brown algæ being almost exclusively marine plants. As one approaches the shore, the attention is often attracted by the green mantle which covers everything overflowed by the tides. This consists largely of the confervoid algæ, which are very abundant and are found almost everywhere. They are dense tufts of fine thread-like plants, often matted at the base; sometimes they are sponge-like, floating masses. The =Ulvaceæ=, the plants next higher in order, are the first which assume ribbon- and leaf-like expansions, and usually first engage the attention of the collector. [pg053] In the green algæ are found the extreme forms of one-celled plants. In ^Pleurococcus^ the cell is microscopic in size. In the =Siphoneæ= the plant still consists of a single cell, but it attains large dimensions and develops into forms resembling, in outward appearance, leaf, stem, and root (see /Caulerpa/). Other plants consist of single rows of cells, called filaments (=Confervaceæ=), or of cells arranged in layers or flat surfaces, called membranes (=Ulvaceæ=). ORDER =CONFERVACEÆ=