Dear Darwin

A M. Tulasne has published lately a splendid monograph of Podostemaceæ & says that some species certainly fecundate under water, though others may not do so & some caulescent ones raise their flower stems above water to flower.²

My species were gathered at the end of the rainy season when the streams were very swollen, they grew appressed like Lichens to rocks, only under water & only away from the rocks of the bank, they were covered with minute flowers that are almost sessile—& grow in the most rapid water.

No species grow in the Himalayan rivers, which I consider very curious & suppose to be owing to the great vicissitudes of their temperature. They are found in the Khasia, Mountains of the Peninsula & Ceylon besides America, Madagascar & various other countries. (see Himal. Journals. II. 314 for footnote.)³

Furthermore some species actually cover the whole bottoms of the streams that are never dry & these flower & fruit abundantly

In Kerguelens Land I most particularly attended to Limosella flowering in 2 feet water; with a bubble of air in each corolla & I assume it is the same thing with Podostemon but I have a bottle full in spirits & will examine.

I do not see why the occasional partial drying of a stream might not let some flowers of Podostemon be exposed & be left for you to cross by any means you chuse.⁴

Ever Yrs | Jos D Hooker