274 MORPHOLOGY OF THE ANGIOSPERMS 



Ovular vascular systems seem to be most frequent in certain major 

 taxa — the Ranales, Leguminosae, Amentiferae, Compositae, Contortae, 

 Tubiflorae. They are rare in the monocotyledons — some palms and 

 amaryllids. Further detailed study may change this picture, but a broad 

 distribution throughout angiosperms surely exists. The history of our 

 knowledge of ovular vascular systems parallels that of chalazogamy, 

 which was, at first, believed restricted to so-called primitive taxa, the 

 Amentiferae, but was later found widely distributed among angiosperms. 

 The presence of a vascular supply in the integuments has been believed 

 to be a primitive character, because of an assumption that this vas- 

 cularization was correlated with freedom of the nucellus from the in- 

 teguments, but this correlation is rare, and is found perhaps only in the 

 Amentiferae. 



Integumentary bundles are continuations or branches of the ovular 

 trace which extends through the funicle— and the raphe, if the funicle is 

 adnate to the ovule proper — to the chalaza and toward the micropyle. 

 The simpler conditions are those where the funicular bundle is con- 

 tinued, unbranched, to the chalaza (Figs. 104A, G and 105E), or be- 

 yond the chalaza to the micropylar region. Where it is branched, the 

 branching may be simple or complex — of successive, more or less 

 pinnate, laterals on a main bundle, or the bundle may break up into a 

 few or several branches in the chalaza; a "crown" or "nest" may be 

 formed below the nucellus, with few or many major branches extending 

 up into or through the integuments. A mesh work of fine bundles may 

 sheathe the nucellus (Fig. 105D). Within genera, and often within 

 families, the pattern of the integumentary vascular system is apparently 

 constant; in other families, such as the Leguminosae, Oleaceae, Com- 

 positae, there is a series from no vascular bundles to an abundant, 

 complex supply. But when angiosperms, as a whole, are considered, 

 there is no evidence of consistency in number of bundles, type of 

 branching, or distribution around the ovule. 



The vascular bundles are usually restricted to the outer integument 

 where there are two integuments; very rarely are they known to occur 

 in the inner integument ( Figs. 104B, C, and 105H, 7 ) , as they do in the 

 Euphorbiaceae. Where vascular bundles are present in the inner in- 

 tegument, they have been described as running first through the outer 

 integument and then entering the inner. If this description is accurate, 

 it provides evidence that the vascular tissue of the integuments has no 

 morphological significance. The bundles are simple, histologically; the 

 xylem consists of a few annular and spiral elements, and there is little 

 or no distinguishable phloem. The bundles end freely in the median or 

 distal part of the integument or, less commonly, form a meshwork, as 

 do veinlets in leaves and sporophylls. 



