Cases the reduction goes still farther and the ascogenous hyphae instead of developing from the ascogonia are derived directly from the vegetative hyphae.
In other lichens we should expect to find the ascogenous hyphae arising directly from the vegetative hyphae as in Humaria rutilans among the ordinary fungi, where the process is associated with the fusion of vegetative nuclei.
In the simplest case the stroma, after bearing its crop of conidia or oidia, develops ascogenous branches in the loosened meshes of its interior (e.g.
Thus in Penicillium, Eurotium, Erysiphe, &c., hyphal ends which are the initials of ascogenous branches, are invested by closely packed branches at an early stage of development, and the asci develop inside what has by that time become a complete investment.
The ascocarps can be distinguished into two portions, a mass of sterile or vegetative hyphae forming the main mass of the fruit bod y, and surrounding the fertile ascogenous hyphae which bear at their ends the asci.
When the ascogonium (female organ) is present the ascogenous hyphae arise from it, with or without its previous fusion with an antheridium.
In other cases the ascogenous hyphae arise directly from the vegetative hyphae.
The asci may be derived from the terminal cell of the branches of the ascogenous hyphae, but usually they are derived from the penultimate cell, the tip curving over to form the so-called crozier.
Concerning the second question, the recent investigations of Buchner ascogenous hyphae with their asci represent the sporophyte since they are derived from the fertilized ascogonium.
S, Ascogenous filaments.
The cytological details of development of the perithecia are not well known; most of them appear to develop their ascogenous hyphae in an apogamous way without any connexion with an ascogonium.