Organography of plants, especially of the archegoniatae and spermaphyta . ger than the whole surface of the cylindric branchedleaves. It is well known, however, that light increases transpiration. Whilst I have not observed in Hakea trifurcata any transition betweenentire and divided leaves, such gradations are found in abundance in otherspecies of Hakea, for example H. pectinata. It is not possible, however, tobring all the manifold leaf-forms of the Proteaceae severally into relation-ship with their life-conditions ; to do this would require not only full know-ledge of the conditionsof life,
Organography of plants, especially of the archegoniatae and spermaphyta . ger than the whole surface of the cylindric branchedleaves. It is well known, however, that light increases transpiration. Whilst I have not observed in Hakea trifurcata any transition betweenentire and divided leaves, such gradations are found in abundance in otherspecies of Hakea, for example H. pectinata. It is not possible, however, tobring all the manifold leaf-forms of the Proteaceae severally into relation-ship with their life-conditions ; to do this would require not only full know-ledge of the conditionsof life, but also of thewhole organization ofthe plants in the same ex-ternal conditions theleaf of one plant, whichthrough the activity ofits root-system obtainsless water, maybe xero-philous, that of another,which through theactivity of its similarorgans receives morewater, is not xerophi-lous. I specially drawattention to this becausein recent times ques-tions of adaptations Fig. 102. Hakea trifurcata, Lower leaves simple flat; upperleaanched branched cy eaves have been frequentlytreated in a one-sidedmanner on the basis of an investigation of a single organ. LEAF-FORM IN EUROPE. I n Europe comparatively few plants possess bilateral or radial leaves. Amongst plants with bilateral ones, however, we must notice the so-called compass-plants \ which bring their leaves, which have a similar leaf-construction on both sides, into the profile-position under intense insolation,and also a number of marsh-plants—the sword-like leaves of Iris, whosedifferent species, but by no means all, live in wet places, and those of Acorus See Stahl, Uber sogenannte Kompasspflanzen, in Jenaische Zeitschrift fiir Naturwissenschaften,XV (1881) ; Heinricher, Uber isolateralen Blattbau mit besonderer Beriicksichtigung der europaischen,speciell der deutschen Flora, in Pringsheims Jahrblicher, xv (1884). Further literature is cited byHaberlandt, Physiologische Pflanzenanatomie,
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