Rhizoidal hyphae

The thallus of homoiomerous lichens is fastened to the substrate by the basal hyphae. The same simple way of attachment also is found in some heteromerous lichens. The rhizoidal hyphae, which anchor the thallus by clasping little particles of the substrate, are like the tomental hyphae. Lichens growing on soil incorporate grains of sand between the hyphae of the lower part of the thallus. 

The thallus of foliose lichens is formed by flattened lobes, which are heteromerous and dorsoventral in structure. Two principal types, the laci-niate and the umbilicate growth form, can be distinguished. Laciniate thalli adhere more or less firmly to the support on which they grow. Either the whole lower surface is in contact with the substrate or the margin of the lobes becomes free and bends upwards. The thalli are usually attached by rhizines or rhizoidal hyphae. The umbilicate lichens are platelike and attached by a central discoid holdfast called the umbilicus (Fig. 47). 

The typical vegetative structure of mold consists of individual hyphal elements (collectively called the mycelium). Hyphae are of three types (1) penetrative hyphae called rhizoids which serve to enter the substrate and glean and transport nutrient (2) stolons, of larger diameter than rhizoids, which serve to link the mycelial mass, and (3) aerial asexual reproductive hyphae, the conidiospores or sporangiosphores. Depending on the organism, asexual spores may be produced within a enclosed structure, the... 

Fig. 16. Special kinds of adaptations to the desert environment in South Africa (A) Lecidea crystallifera cross section of the thallus. P, cortex cone Pi, pigment stratum Go, chains of phycobionts Py, pycnoconidia O, aperture of the pycnoconidia M, medulla Rhi, rhizinic hyphae Rz, rhizoidal string. (B) Buellia sp. on a quartz block. I, general view of the thallus on the quartz (natural size) II, cross section of the thallus III, model of the course of light to the phycobionts of the inverse thallus. (Ap, apothecium S, hyphae with soil particles An, groups of phycobionts Go, phycobiont layer Q, quartz L, incident light B, thallus. (From Vogel, 1955.)...

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