Order 17. =Cutleriaceæ.= The thallus is formed by the union of the originally free, band-shaped shoots. The growth is intercalary. Sexual reproduction by the conjugation of male and female gametes. An asexual generation of different appearance, which produces zoospores, arises from the germination of the zygote. _Cutleria_, _Zanardinia_. Sub-Family 2. =Acinetæ.= Branched, simple cell-rows with intercalary growth. The organs of reproduction are partly uni-and partly multicellular; in the unicellular ones a cell without cilia is formed, which may be destitute of a cell-wall, but has one nucleus (oosphere?), or which has a cell-wall and contains several (generally four) nuclei (aplanospores?); in the multicellular, monosymmetric swarm-cells with two cilia (spermatozoids?) are formed. The fertilisation has not been observed. Order 1. =Tilopteridaceæ.= _Haplospora_, _Tilopteris_. Family 2. =Cyclosporeæ.= The individuals are multicellular, with growth by an apical cell. The thallus--often bilateral--is differentiated into a root-like structure (attachment-disc), and stem, sometimes also into leaves (_Sargassum_). Sometimes a differentiation occurs into various tissue-systems, viz. an external assimilating tissue, a storing tissue, a mechanical tissue of thickened, longitudinal, parenchymatous, strengthening cells, and a conducting tissue of sieve-cells, or of short sieve-tubes with perforated walls. Colouring material, as in Phæosporeæ. Vegetative reproduction can only take place by means of detached portions of the thallus (_Sargassum_), which are kept floating by means of bladders (Fig. 70 _A_, _a_, Fig. 72). Zoospores are wanting.