sentences:  This would have resulted in greater transpiration rates and gas exchange, but especially at high concentrations, large leaves with fewer stomata would have heated to lethal temperatures in full sunlight.Increasing the stomatal density allowed for a better-cooled leaf, thus making its spread feasible, but increased CO2 uptake at the expense of decreased water use efficiency.The rhyniophytes of the Rhynie chert consisted of nothing more than slender, unornamented axes.