Trunk woods of Early Carboniferous Protopitys buchiana show the earliest example of
tylose formation and the first record for a progymnosperm. Protopitys
tyloses are more densely located in inner trunk woods and near growth layer boundaries. We suggest, therefore, that an altered physiological state of living ray cells, during dormancy and/or following
water stress, was necessary to make the woods vulnerable to
tylose formation. Coupled with the distribution and proximity of abundant wood ray parenchyma to large xylem conducting cells, the positions of conduits filled with
tyloses can be interpreted as ecophysiological responses of the plant to changes in local environment. In addition, some xylem conducting cells might have functioned as vessels. Fungal hyphae are present in some tracheary cells and in some areas with
tyloses, but there is no evidence for wood
trauma; we conclude, therefore, that these particular cases of
tyloses are probably not induced by
wound trauma. Protopitys buchiana wood thus shows structure/function similarities to modern woods with vessels, such as those of dicot angiosperms. This implies that ancient and modern plant ecophysiological responses correlate well with the physical parameters of their cellular construction.