1921] ARBER—LEAVES OF HELOBIEAE 37 
The third and last leaf type, that in which there is a differenti- 
ated blade, occurs in five of the seven families, the exceptions 
being the Juncaginaceae and Naiadaceae. It is not necessary 
here to discuss the evidence, based partly on a study of the suc- 
cession of leaf forms in the ontogeny, and partly anatomical, which 
has led to the conclusion that these blades are ‘‘pseudo-laminae,”’ 
originating by the expansion of the apex of the petiolar phyllode, 
for this question has been considered elsewhere (1, 6). The 
present paper adds a study of the significance of the blade venation 
of the Alismaceae. 
The final impression left by this survey of the leaves of the 
Helobieae is that there has been a remarkable parallelism of develop- 
ment within the different families. The three leaf types enumerated 
recur throughout the cohort in forms which, although modified in 
various ways, are identical in essentials. 
Batrour LABORATORY 
CAMBRIDGE, ENGLAND 
LITERATURE CITED 
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Roy. Soc. B. 91:96-103. r9r9. 
, Leaf base phyllodes among the Liliaceae. Bot. GAZ. 69:337-340. 
1920. 
4- , Tendrils of Smilax. Bort. Gaz. 69:438-442. pl. 22. 1920 
5- , On the leaf structure of certain Liliaceae, considered in relation to 
the phyllode theory. Ann. Botany 34:447-465. 1920 
———, Water plants: a study of aquatic Angiosperms. Cambridge 
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Baker, J. G., and Grant, J. A., The botany of the Speke and Grant 
expedition. Trans. Linn. Soc. 29:1~190. 18 
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9- Domnin, K.., iiber die Stipular- 
bildungen. Ann. Jard. Bot. Buit. “24: 3117-326. pls. IT. 191t. 
7 
to. Ernst, A., Uber Stufengang und Entwickelung der Blatter von Hydrocleis 
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11. HiERonyMus, G. 
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