BOTANICAL GAZETTE. 286 



margin. In typical P. tirmula they are usually quite similar to those 

 found in P. treinuloides, though sometimes more widely separated. Some 

 specimens of this species failed to show any glands; and a cultivated 

 ])lant of the drooping variety was once examined m early May without 

 the detection of a single gland, though at other times, these organs 

 were found in abundance on tliC same plant The glands oi P. tricJw- 

 carpa are quite variable, being sometimes large and close together, at 

 other times, small and widely separated. I was never certain that I 

 saw these bodies on P. alba, though they may sometimes occur as 

 very small outgrowths concealed by the wool which is so abundant 

 on the leaves Small serration glands occur on P. an^ustifolia, and 

 the lowest pair — corresponding, doubtless, to those found at the top of 

 tlie ]jetiole in so many species — are no larger than the others. On P. 

 Ere/iioniii very small glands were occasionally seen, but appear to be 

 uncommon. In P. iii^^ra serration glands are evident and the lowest 

 pair much as in P. angiistifolia. No basal glands were seen on the 

 var. dilatata ; nor were any found on P. totnentosa. It appears, there- 

 fore, that the greater part of the species examined possess two or more 

 distinct or confluent, well formed glands, situated where the blade 

 and petiole join; and in the few species where none were discovered. 

 I am by no means sure that they may not occasionally be produced; 

 for, as has been previously stated, a careful examination of a plant of 

 the drooping P. Uemiila — which, by the way, was sent out by nursery- 

 men as P. graudidentata, pendula — in early May, failed to show a 

 single gland, but, a week or two later, after several days of rain, the 

 young branches grew very rapidly for a short time, unfolding many 

 new leaves, and the first three or four of these on each branch 

 bore large and active glands. 



Though of such frequent occurrence, these glands have been 

 generally overlooked or considered of little value by systematic 

 botanists, probably because of their limitation to the earlier leaves, 

 and their occasional entire suppression. The elder Michaux, speak- 

 ing of this genus', says: "Glandule basi folionum nihil valent ad dis- 

 tinguendas species, quidpe quae, in eadem specie, aut desunt aut ad- 

 sunt." In his descriptions of the species he mentions these organs 

 only in P. graiuiidcutata. The younger Michaux figures them in /'. 

 angiilatd^ and /*. inonilifcra^ without making mention of them while 

 they are figured and mentioned under P. canadensis (P. moniliferay . 

 Wesmael,' speaking of P. Candkans, says "Petiole * * * por- 

 tant 2 glandes dans le jeune age." Bigelo^v* and Loudon' men- 

 tion the glands of P. grandidcntafa : and Pursh** describes them 

 in P. hevigata {P. nionilifera), and P. 7?wnilifera. Loudon" also 



' Floi;i l)oie;ili Aincricanrt, II, 24:1 



■' Arbcs, III PI. XI; N. Am. Sylva, II, PI. !)4. 



■■' Avbri's, III, V\. X; N. Am.Sylva, II. PI. m. 



4 Aihivs, III, p|.. 2!)«, 20!t, PI. XI ; N. Am. Sylva II, p. 117, PI. il."). 



^ MonoLrrnpliic de toutcs Ics especes counucs du genre Popiilus, 1H09, p. 08. 



•i Plants (if P.osKin, 1S24, p. :!70. 



7 Arboretum, III, 11. IGoO. 



" N. Am. Flora, 1814, p. 018 and 61«». « 1. c. pp. IO-'m and IGoT. 



