THE OVULE 259 



to the micropyle, rather than obstruct its entrance there, as has been 

 suggested. Basal appendages are present on ovules of some taxa, as in 

 Tetratheca, where these projections are prominent, and lateral projec- 

 tions characterize some of the borages. 



Fusion among the parts of the ovule — as among other organs — is com- 

 mon and is recognized as an advanced condition. Commonly, the in- 

 teguments are fused to one another and to the nucellus for various 

 distances, and the fusion is congenital. Lines of demarcation between 

 these fused parts are usually absent. Freedom of the nucellus from the 

 integuments, as in Casuarina, Mijrica, Juglans, JuUunia, Cleome, Can- 

 anga (Fig. 98C), is probably rare. Freedom of the integuments from 

 one another — though they may lie appressed together — occurs in some 

 of the more primitive dicotyledons, especially certain genera of the 

 Rosaceae, Leguminosae, Capparidaceae, Ranunculaceae, some of the 

 Amentiferae. All stages of fusion of the integuments are seen in other 

 genera of these families — Spiraea, Lupiniis, HeUebonis. Rarely, integu- 

 ments are separated by a space on the chalaza. The palms show all 

 stages in fusion of the two integuments — from two entirely separate 

 structures to one with no evidence of the fusion. Also, rarely, the outer 

 integument fuses over the nucellus, closing the micropyle except in the 

 inner integument, as in Qiiercus, AlchemiHa, Sibbaldla. This closure has 

 been interpreted as the result of loss of function under chalazogamy or 

 parthenogenesis. Anatropous ovules with two integuments usually show 

 only one integument on the side adjacent to the funicle; fusion of the 

 outer integument and the funicle is congenital, and histological evi- 

 dence of the union is lacking. 



Two integuments clearly represent more primitive structure than 

 one. The single integument in many — probably the great majority — of 

 taxa represents, morphologically, a fusion of the two integuments. Most 

 taxa with two integuments show connation at least in the lower parts. 

 Many with a single integument show evidence of double nature at the 

 tip, but the fusion is usually congenital and there is no histological 

 evidence of the union. There are rare exceptions, as in HeUebonis, 

 where cell arrangement shows doubleness of the integument. It has 

 been argued that the single integument represents the primitive condi- 

 tion, probably because it is the simpler condition and because, in the 

 higher dicotyledons, it is derived, ontogenetically, "from the epidermis 

 alone," whereas the outer integument is subepidermal in origin. But 

 fusion, where congenital, produces false simplicity of form, and reduced 

 structures do not retain the same histological origin as the unreduced 

 form. Ontogeny alone does not give proof of morphological structure. 

 The single integument may represent either the two integuments in- 

 timately fused or, probably infrequently, one surviving from two. Num- 



