Hemicellulose: a hard carbohydrate somewhat similar to cellulose in walls of 



some algae; more common in cell walls of higher plants. 

 Heterocyst: a specialized cell in some filamentous Myxophyceae which is usually 



larger than and a different shape from the vegetative cells. 

 Heterogametes: sex cells unlike in size, shape, and behavior. 

 Heterothallic: from two different thalli; of reproductive structures or cells 



borne on different parents. 

 Heterotrophic: obtaining food in soluble or particulate form; not photosynthetic. 

 Heterotypic division: reductive division of a nucleus; segregation of chromo- 

 somes. 

 Hirsute: hairy. 



Holdfast cell: the basal cell of a filament modified to form an attaching organ. 

 Holophytic: obtaining food by photosynthesis. 

 Holozoic: ingesting food Uke an animal. 



Homothallic: from similar thalli; of gametes from the same parent. 

 Homotypic division: nuclear division (mitosis) involving a splitting of chrom- 

 osomes; the chromosome division immediately following first meiotic 

 division. 

 Hormogonium, Hormogone: a fragment of a filament; a short section broken 



away from a mature trichome (Myxophyceae). 

 Hormospore: a vegetative spore-like body formed from a short section of a 



filament that becomes invested by a thick membrane. 

 H -shaped pieces: sections formed when a filament of cells dissociates; the H- 

 shaped pieces formed as a result of the fact that cell walls are in two 

 pieces which overlap in the midregion, the line of cleavage being here 

 rather than at the cross walls of the filament. 

 Hyaline: colorless; transparent. 



Hypocone: the lower part or posterior half of a dinoflagellate below the me- 

 dian girdle. 

 Hypotheca: the lower half of the cell wall of a dinoflagellate below the median 



girdle. 

 Hypovalve: the lower or smaller of the two parts of a diatom cell wall. 

 Hypha, Hyphal filaments: threads which inclose the central, axial filament in 



some Rhodophyceae ( Lemanea ) . 

 Hypnospore: small, thick- walled, asexual spore; especially the spores formed 



undergrovmd in Botrydium. 

 Idioandrosporous: having androspores formed in filaments separate from those 

 in which the female organs (oogonia) are produced (e.g., in Oedogonium) . 

 Imbricate: overlapping; joined in an overlapping series. 

 Incised: cut, with narrow slits. 

 Indurate: hard. 

 Inferior pore: a pore in the wall in the lower part of an oogonimn (Oedogon- 



iaceae ) . 

 Initial cell: cell which generates other cells, or which gives rise to tissue. 

 Inner fissure: the inner part of the raphe in the pennate diatoms. 

 Integument: a covering, sheath, or envelope. 



Intercalary: appearing between, inserted (as between cells), rather than ter- 

 minal or marginal. 

 Intercalary hands: bands which help to hold the two valves of the diatom 



cell together. 

 Interpolate: to place between. 

 Intestiniform: shaped like an intestine; tubular. 

 Intravitam: within living tissue; e.g., to stain a living cell. 



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