399 BOTANICAL GAZETTE | DECEMBER 
the disposition of the phloem in OQ. regalis, it will be well to 
define a sieve tube. Both Russow and Janczewski have studied 
sieve tubes very carefully, and Poirault has more recently rein- 
vestigated the subject in the vascular cryptograms. The investi- 
gator last named summed up his observations on sieve tubes in 
the roots of vascular cryptogams in the following terms :” 
Les tubes criblés peuvent se rapporter 4 deux types: le premier carac- 
térisé par des cloisons transverses perpendiculaires aux faces principales et 
ne portant qu’un seul crible (¢vfe Courge, Lecomte); le second reconnaissable 
a ses cloisons transverses trés obliques portant d’autant plus de cribles que 
leur obliquité est plus grande (¢yfe Vigne, Lecomte). On trouve, en outre, 
sur les faces longitudinales des ponctuations isolées ou réunies en trés petits 
groupes, constituant rarement des cribles aussi développés que ceux des 
faces transverses. Le contenu de ces tubes est un liquide hyalin tenant en 
suspension de nombreuses sphérules réfringentes, rassemblés surtout au 
niveau des cribles et des ponctuations isolées. I] n’ 'y a pas de noyau. La 
membrane est cellulosique. 
He further adds that two substances occur as a rule — (1) 
the “globules brillants’’ already mentioned, and (2) “les 
bouchons calleux qui font corps avec la membrane et peut-étre la 
traversent entiérement.” 
In dealing with the sieve tubes of the stem and petiole he 
does not point out any other peculiarities, but deals at length 
with the callus plugs, and the perforation of the sieve plates.% 
The observations of Russow, Janczewski, and Poirault agree for 
the most part, except in reference to the callus plugs. 
The following criteria would seem to be distinctive in deter- 
mining the presence of sieve tubes in the Osmundaceae; the 
existence of sieve plates, the absence of nuclei, and the presence 
of ‘‘globules brillants.” Less distinctive and rather as a con- 
firmatory test I have sought for callus. Russow made this test 
one of paramount importance, but it seems best in dealing with 
the vascular cryptogams to give it a second place, and for the 
following reasons: (1) the callus, so-called, in the seive tubes 
™?POIRAULT: Or sur les cryptogames vasculaires. Ann. Sci. Nat. 
Bot. VIL. 18: 138. 1 
3 POIRAULT : of. cit. 191. 
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