THE CARPEL 189 



the primitive type, the type from which have been derived various 

 speciahzed types, such as the achene. (The terms folhcle and achene 

 are usually applied to mature carpels, fruits.) The follicle is primitive 

 in its elongate form, numerous ovules, simple dehiscence, and the fre- 

 quent absence of a style; it is advanced in the delimitation of ovary 

 and stigma. It is characteristic of many genera of the more primitive 

 families of both dicotyledons and monocotyledons. Carpels of the fol- 

 lowing genera have many folliclelike characters: Dcgeneria, Drimijs 

 (sect. Tasmannia), Butomiis, Trolliiis, Calfha, Coptis, Phijsocarpus, 

 Akebia, Telopea, Paeonia, Toficldia, Schcuchzeria. 



Closure of the Carpel 



One of the distinguishing characters of the angiosperms is the en- 

 closure of the ovules by the megasporophyll; the pollen grains do not 

 reach the ovule but germinate at a distance, in contrast with the condi- 

 tion in the gymnosperms, where the ovule is "naked" and the pollen is 

 received and germinates on the ovule. There are exceptions in tlie 

 conifers to the place of germination of the ovule; in Araucaria, Agathis, 

 and Tsuga, the pollen germinates at a distance from the ovule. In the 

 angiosperms, there are taxa in which the carpel is not completely closed 

 at pollination time — Degeneria, Drimijs, Butomaceae, Hydrocharitaceae, 

 Sparganium, Sassafras, Coptis, Tiarelh, Platajius. The "opening" is very 

 narrow, and pollen grains probably never enter the ovarian locule 

 through it. (Pollen has been reported in the stylar canal in Butomopsis, 

 Hillebrandia, Reseda, but probably does not germinate there.) The 

 opening is usually quickly closed but may still be present in the mature 

 fruit. 



"Union" of the carpel borders shows all stages from the presence of 

 an open slit to loosely and tightly interlocking papillae and to histologi- 

 cal fusion — a union so complete that no evidence remains in tissue 

 structure (Fig. 74A, B). In the open carpels of Degeneria and Drimijs, 

 the opening is partially closed by the papillose cells of the stigmatic crest 

 (Fig. 73). In carpels where the uniting margins or borders are closely 

 appressed but without histological union, the epidermal layers may be 

 merely coherent, without elaboration of surface-cell form, but the epi- 

 dermal layers are often rugose or toothed and interlock as they mature; 

 evidence of the identity of the individual layers may be only in cell 

 form and position. Ontogenetic adjustments among the uniting layers 

 often obscure the line of fusion. All these conditions are found in 

 carpels in which union is ontogenetic; where fusion is congenital, there 

 is no histological evidence of the union. Morphological nature of the 

 carpel may be evident in the maturing and mature fruit, as in the peach 

 and cherry. 



