In the present paper biological and ecological studies are made of two Podostemonaceae, namely Apinagia Accorsii Toledo (n. sp.) and Mniopsis Glazioviana Warmg. which live attached to the rocks of Piracicaba's fall. (At Piracicaba, E. de S. Paulo, Brasil). For revelling great modification in all vegetative parts aside from many regression characters as reduction of the conducting system, absence of stomata, simplification of the structure of the caules and leaves, prevalence of vegetative propagation and so forth special reference is made to Apinanagia Accorsii Toledo. All the observation refer to a period a little longer than an year, comprising the vegetative and floral cycles. The local distribution of both the species is the following: 1 - Apinagia Accorsii Toledo in the rocks situated just in the water fall where velocity ad aeration of the liquid are very high. 2 - Mniopsis Glazioviana Warmg. in the rocks some dis- tance upwards in the current. Out from the water the Podostemonaceae very soon will dry up and die, specially if they are directly under the action of the sun rays. The plants flowrish and fructify only when in contact with the air. Pollinization is direct. Notwithstanding the complete destruction of the whole vegetative part due to a prolonged exposition to the air (in the dry period) the fruits attach themselves to the rocks by means of a pedicel. In Apinagia Accorsii the buds having from 3 to 8 flowers are embedded in a flat rhizome. Externally they are recovered manecerão fixos à rocha; no próximo período de enchente as sementes germinarão nos meios apontados, garantindo, assim, a perpetuação da espécie no habitat. A polinização de ambas as espécies, de acordo com as observações feitas, é direta, realizando-se em plena atmosfera, quando as anteras enxutas e suficientemente dessecadas sofrem a deiscência, libertando o pólen. A espécie Mniopsis Glazioviana Warmg- comporta-se de igual modo que Apinagia Accorsii Toledo sob o aspecto referente à ação entre planta e habitat. with two imbricate scales. The rhizomes of Apinagia give rise to transitory caules of frondiform nature ramified and terminated by many capillaceous lacinias. After the detachament of the caules the corresponding scars can be seen on the rhizomes. The vegetative propagation of Apinagia is performed by hemicyllindrical stolons attached to the surface of the rocks, which by a process of tuberization produce laterally and alternately new rhizomes disposed in an increasing order up from the extremity. The plants of Mniopsis, on the contrary, produce hemicyllindrical roots from whose flanks radicular buds give rise to folliaceous formations disposed into pairs. According to our observation the proper means for seed germination are: 1 - The placent of parcially open fruits. 2 - The external and internal walls of the open capsules. 3 - The pedicel of the fruits, the rest os Apinagia's rhizomes and finally vegetative residues of Mniopsis. The embryo, charged with chrorophyll at the time of germination of the seeds, is a microscopical structure provided with two long cotyledons. The radicule and caulicule are indistinct. In the seedlings the extremity of the hypocotyl develops a fascicle of unicellular hairs, whose principal function seems to be fixation. Due to the weight of the fruit and the flexibility of the pedicel the capsules charged with the seedlings establish, under the action of the flow, contact with the rock's surface thus allowing the young plants to attach themselves more and more to their definitive substratum.