1958] 



ANATOMY OF GUAYANA MUTISIEAE — PART II 



183 



wood structure (Carlquist 1957b) and Chimaiitaea-like stem anatomy. Such in- 

 stances- as these suggest the common origin of these genera, followed by in- 

 dependent changes in various anatomical and morphological characters. 



The significance of certain anatomical characters is not at present clear. For 

 example, although trilacunar nodes are considered primitive in most instances 

 (Sinnott 1914), the genera Stenopadus and Gongylolepis have multilacunar 

 nodes, as do Heliantheae which are best regarded as primitive (Carlquist 

 1957d). The excessive sclerenchyma present in mutisioids studied here seems 

 characteristic of the tribe, except for herbaceous genera, although it is difficult 

 to designate it as primitive or advanced. The distribution of secretory canals 

 and laticiferous cells in Mutisieae is curious, and further knowledge of the 

 distribution of these within the family is required before we can be sure that 

 the frequently accepted idea that secretory canals are primitive and laticifers 

 advanced is of general application in the family. The possibility remains that 

 some Compositae never acquired secretory canals, so that in Guayana Mutisieae 

 we would be witnessing an early stage in their formation, as may be the case 

 with laticifers in the Guayana Gerberinae. 



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