. Fungi, ascomycetes, ustilaginales, uredinales. Fungi. 8o PLECTOMYCETES [CH. enter the stomata, extend through the intercellular spaces and send haustoria into the neighbouring cells, and in Erysiphe (or Oidiopsis) taurica the whole mycelium during the conidial stage is located in the tissues of the host. We have thus, within the limits of the family, a transition between ecto- and endoparasitism through hemiendophytic forms, and forms which are endo- phytic under abnormal conditions. When perithecia are about to be produced and the mycelium emerges and spreads over the surface of the host le
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. Fungi, ascomycetes, ustilaginales, uredinales. Fungi. 8o PLECTOMYCETES [CH. enter the stomata, extend through the intercellular spaces and send haustoria into the neighbouring cells, and in Erysiphe (or Oidiopsis) taurica the whole mycelium during the conidial stage is located in the tissues of the host. We have thus, within the limits of the family, a transition between ecto- and endoparasitism through hemiendophytic forms, and forms which are endo- phytic under abnormal conditions. When perithecia are about to be produced and the mycelium emerges and spreads over the surface of the host leaf, the hyphae both oiPhyllactinia and oi E. taurica show haustorial branches (ad- pressoria), though no haustoria are produced. It may be inferred that the ectophytic condition with haustoria penetrating the epidermal cells is primi- tive in the group. Indian and Persian specimens of E. taurica have been found under practically desert conditions, others have been collected on plants of the steppes of Turkestan at a height of 6000 feet, and in localities exposed to very dry winds. The suggestion has consequently been made that the endophytic habit in this family is an adaptation to xerophytic conditions, since it both provides shelter for the developing mycelium and obviates the necessity of piercing through the cuticle, which in desert plants is of considerable thickness. The Erysiphaceae are propagated during the summer by rather large oval uninucleate conidia (fig. 38). These are ordinarily produced in rows on simple conidiophores with one or more basal cells. In the endophytic E. taurica, however, the conidia are borne singly on branched conidio- phores which emerge through the stomata of the host. In the case oiPhyllactinia Cory- lea, which is met with on a large number of deciduous trees, variations occur in the shape of the conidia borne on different hosts, and indicate the existence of morphological dis- tinctions between the biological forms of the species. Before the