Fresh- Water Sponges From Mexico. i6i 



hemisphere and only be found the second time at its own antipo- 

 des is indeed remarkable. 



The lower reaches of the Colorado of the West extend lor miles 

 through a region described by the collector as 'the hottest, driest, 

 and most barren in the United States,' whose 'vegetation consists 

 of mesquit, cacti, and the screw-bean, Strombocarpus pubescens.' 

 Its normal border lands are known as the 'first' and 'second' 

 ' bottoms,' of which the latter is the higher and of course more 

 distant from the channel. By the frequent changes in its bed hdw- 

 ever. the river cuts through these, and. washing away the one and 

 filling up the other, reverses their physical conditions- Upon the 

 ' second bottoms,' then, said to be only reached to any consider- 

 able depth by the annual floods occurring during parts of May 

 and June, and not to continue flooded more than six weeks at a 

 time, the screw-bean abounds. It is described as a small tree of 

 the general appearance of a peach tree, but with more slender 

 drooping branches. More or less of an alkaline deposit whitens 

 the ground upon which they grow, and the approaching traveler 

 is puzzled to see in strong contrast with it hundreds or even 

 thousands of dark masses, ' like wasp's nests,' suspended two or 

 three feet above. 



It was this conundrum that confronted Dr. Palmer during his 

 recent visit, and the answer we have in the spong(^ before us. 

 From the Amazon River in the tropics to the waters of Maine 

 and Nova Scotia in the temperate regions ot the north, sponges 

 have long been known to aflect the pendent branches of stream- 

 bordering bushes; but it is unlikely that they have ever before 

 been observed in such quantities suspended for nine or ten months 

 of the year over land parched and desolate. 



On referring to the earlier descriptions of his discoveries by H. 

 J. Carter, Esq., F. R. S., we find that though he collected this 

 species on two or more occasions, the fragments were always 

 found detached from their place of growth and floating upon the 

 surface in the water- tanks referred to, about one month after the 

 rainy season had commenced. He believed that the vitality of 

 the gemmules was preserved during the dry season, notwithstand- 

 ing their exposure to the sun and dessicating winds, and that 

 their germination after the water had again reached them was 

 followed by a very rapid growth of new sponge. This would 

 seem to have been the case also with the present variety, as. 

 according to the reports of the collector, the masses could not 

 have been submerged for a greater period than six weeks in any 

 one year. Whether the whole bulk as now seen was attained 

 during a single season, or is the cumulative result of several 

 annual growths of the persistent masses, cannot now be deter- 

 mined. 



It is worthy of notice that M. plumosa and this variety Palmeri, 

 differ from all other known fresh -water sponges by the presence 



