A few lichens among Graphidineae and Pyrenocarpeae grow in a united body generally looked on as a stroma; but Wainio[545] has demonstrated that as the fruiting bodies give rise to this structure by agglomeration—by the cohesion of their margins—it can only be regarded as a pseudostroma. Two British genera of Pyrenolichens, _Mycoporum_ and _Mycoporellum_, exhibit this pseudo-stromatoid formation. [Illustration: Fig. 90. A, entire perithecium of _Porina olivacea_ A. L. Sm. × ca. 40; B, dimidiate perithecium of _Acrocordia gemmata_ Koerb. × ca. 20.] C. DEVELOPMENT OF REPRODUCTIVE ORGANS As most known lichens belong to the Ascolichens, the study of development has been concentrated on that group. Tulasne[546] was the first to make a microscopic study of lichen tissues and he described in considerable detail the general anatomical structure of apothecia and perithecia. Later, Fuisting[547] traced the development of a number of perithecia through their different stages of growth, but his most interesting discovery was made in _Lecidea fumosa_, a crustaceous Discolichen with an areolate thallus in which the apothecia are seated on the fungal hyphae between the areolae. In the very early stages represented by a complex of slender hyphae, he observed an unbranched septate filament with short cuboid cells, richer in contents than the surrounding filaments and somewhat similar to the structure known to mycologists as “Woronin’s hypha,” which is an ascogonial structure. These specialized cells disappeared as the hymenium began to form. 1. DISCOLICHENS [Illustration: Fig. 91. _Collema microphyllum_ Ach. Vertical section of thallus. _a_, carpogonium; _b_, trichogyne. × 350 (after Stahl).]