2^7 BOTANICAL GAZETTE. 



speaks of their occurrence on the latter species, and Wesmael,'" 

 speaking of this species under its synonym of P Canadensis, 

 also mentions these bodies; and elsewhere" makes the fnUowing 

 surprising statement: "Communement sur les feuilles des fem- 

 elles on recontre deux glandes petiolaires ires-voisines de la base 

 du limbe. Toutefois, ce caractere n'a rien de constant sur toute des 

 feuilles d'un meme rameau, et quelquefois meme on les observe sur les 

 feuilles de I'autre sexe." Pursh'^also noted the g\^^\ds oi F. trepida 

 {P. tremidoides). As I have said, the secreting and subjacent tissues in 

 these organs arc charged, while young, with syrup, the suear being 

 doubtless derived from the transformation of starch which is oi 

 abundant occurrence in the adjacent parenchyma. A study of glands 

 at the beginning of their activity showed the process of secretion to be 

 the followmg: The slight cuticle which covers the modified epidermis 

 becomes separated frpm the balance of the cell wall, probably by 

 the transformation of a thin layer of the latter into one of the gums, 

 which by its osmotic power causes transudation of saccharine fluid 

 from the interior of the cell. This constantly increasing quantity of 

 fluid swells the loosened cuticle out in the form of a delicate bladder, 

 which soon bursts and allows the nectar to appear on the surface. 

 Evaporation is constantly going on, so that, if the plant is supplied 

 through its roots with an abundance of water the cell wall separates 

 a denser external, from a less dense internal syrup and a continuation 

 of the osmotic action keeps up the secretion of nectar for a consider- 

 able length of time. At times the evaporation predominates, and 

 crystals of sugar may then be found upon the gland, in a dense, un- 

 crystallized syrup; at other times the secretion is so plentiful as to 

 collect in drops which occasionally flow upon the surface of the leaf. 

 Carefully washing the glandular surface with pure water always lessen- 

 ed its power of secretion, and, if repeated several times, so as 

 to remove the last trace of sugar, completely prevented further 

 activity. The addition of a small drop of syrup, however, 

 always caused a renewal of the secretion, in glands which 

 had been thus washed.''^ 



Although the presence of apparently perfect glands was noticed in 

 the species previously enumerated, I was able to prove their activity by 

 examination of living jjlants only in P. tvcinuloides ; P. bahamifcra, can- 

 dicans ; P. grandidentata ; P. mouilijera ; and P. tremiila, pcndiila. 



The nectar which accumulates at the surface of the glands is 

 largely gathered by numb'^rs of small insects, chiefly Hymenoi}tera and 



1" i. r. p. fi3. 

 . '1 1. c. p. 27. 



12 ]. c. p. 618. 



i'^ These experhnents, which appear to show conclusively the osmotic 

 nature of the secreting process, were sugL^ested by, and are hut repetitions of, 

 .some of those performed by Dr W. P. Wilson in Pfetler's laboratory, the re- 

 sults of which were communicated to the writer last winter, and have just 

 been published in Untci'HUclomqot aus d. hot. Iiid.iii Tnchiiujcii,, as I learn from 

 an abstract of Dr. Wilson's article by Francis D-Axvi'm {Hot . ZcitKiirj, ISHl, 

 p. 545). 



