J. H. Long — Polarization of Tartrate Solutions. 351 



a matter that may well excite our wonder that, migrating 

 such immense distances from their places of origin, through 

 every phase of soil and climate — through all the zones of 

 the Eastern Hemisphere, and now, as we learn from this 

 group of Honduras plants, through the New World — they 

 marched, holding so firmly to their original group of charac- 

 ters, generic and specific, that wherever we open their tombs 

 we recognize them instantly as old friends. In their long 

 marches some perished by the way, and here and there their 

 numbers were recruited by new forms, imported or developed ; 

 but the leading members of the troop, in virtue of some occult 

 protection against outside influences, preserved almost without 

 alteration all the complicated characters of their vegetative and 

 reproductive systems. 



We shall look now with eagerness to South America for the 

 identification there of this Mesozoic flora, which we have found 

 in full development in Virginia, New Mexico, Sonora, and now 

 in Honduras. It had before been recognized in Australia — 

 where it seems to emerge from the Paleozoic flora and perhaps 

 began — New Zealand, India, Tonquin, China, Turkestan, and 

 various parts of Europe. 



Hence, with its discovery in South America we shall see it 

 reaching as a girdle around the entire globe. This girdle was 

 not put around the earth, however, like Puck's, in forty min- 

 utes, but in thousands and millions of years; for when we 

 realize with what slowness the migration of plants takes place, 

 we must recognize in the universal distribution of the Carbon- 

 iferous and Mesozoic floras evidence of the lapse of intervals of 

 time of which the duration is simply immeasurable to us. 



Aet. XXXVIII. — On the Circular Polarization of certain 

 Tartrate Solutions. I. By J. H. Long. 



The change in the circular polarization of a solution of an 

 active substance by admixture with an inactive one has been 

 studied in several cases. Muntz found, for instance, that the spe- 

 cific rotation of cane sugar for a concentration of 20 gm in 100 cc 

 changed from [a] D = 66*°5 to [«] D = 66*°3 by addition of 5 gm 

 of NaCl, and to 61 -°0 by addition of 20 m .e 



The same chemist and others have shown the effects of add- 

 ing various substances to sugar solutions. In most cases a de- 

 crease in the specific rotation was found. 



Under certain circumstances the addition of an inorganic 

 substance converts an inactive organic body into an active one, 

 as in the case of mannite when in solution with alkalies, weak 



