prothallus-tissue was found with an apical ‘tent-pole’ protuberance. A striking feature of _Conostoma_ is the mechanism for the reception of the microspores. The free part of the nucellus consists of the plinth, a broad tapering region originally filled with parenchyma but in most cases represented only by its epidermis: the plinth, _p_, is seen in fig. 494, B, to be two-storeyed, the upper and narrower storey being a space formerly filled by a pad of tissue suspended from the floor of the superposed lagenostome (pollen-chamber)[835]. The greater development of the domical plinth is a feature in which _Conostoma_ differs from _Physostoma_. At the apex of the plinth and resting on a slight depression is a small lagenostome, bowl-shaped in section, and like the pollen-chamber of _Lagenostoma_, formed as the result of enzyme-action on the apical papilla of the nucellus (fig. 494, B, B′, _l′_). The mouth of the lagenostome engages with the micropylar tube by a projecting flange (fig. 494, B′, _f_) of tissue lining the micropylar canal and by a second flange (_f′_) at the base of the lagenostome where the roof of the plinth (fig. 494, B′, _p_) bends downwards and inwards. The walls of the lagenostome are formed by strong cells with thickening bands giving them the appearance of tracheids (_l′_), but the floor of the lagenostome is made of thinner cells which become disorganised, allowing the microspores to fall into the large plinth-cavity below (_p_, fig. 494, B), an arrangement comparable with the two-storeyed pollen-chamber of _Bowenia_[836] and, to a less extent, with the micropyle of the Conifer _Tsuga_. The microspores are multicellular and ellipsoidal measuring 75μ × 65μ. [Illustration: Fig. 494. A, _Stephanospermum akenioides_; _s_, space between integument and nucellus; _n_, nucellus; _e_, inner part of testa; _sc_, sclerotesta; _t_, _t_, tracheidal mantle; _pc_, pollen-chamber; _a_, archegonia; _td_, tracheidal pad. B–D, _Conostoma oblongum_; _a_, level of the transverse section shown in fig. C; _b_, level of transverse section D; _m_, lobes of tissue surrounding the micropyle; _sa_, sarcotesta; _v_, vascular bundles; _p_, plinth. B′, section of lagenostome and part of the integument; _f_, _f′_, flanges; _l′_, wall of micropyle-funnel. E, F, G, _Gnetopsis elliptica_; _t_, tent-pole. F, section of the plumes. G, section through the lagenostome. H, _Gnetopsis_ from Barnsley, Yorkshire, slightly enlarged. I, _Physostoma elegans_; _h_, hairs. K, L, _Mitrospermum compressum_; _cf_, inner flesh; _n_, nucellus and megaspore. L, transverse section. M, microspores and (?) male gametes of _Physostoma elegans_. N, microspore of _Physostoma_ showing part of exine and the internal cells. (A–I, N, M, after Oliver; H, Kidston Coll. No. 1255; K, L, after Mrs Arber.)]