THE CARPEL 223 



valuable factual material for the interpretation of flower morphology. 

 The publication of the theory appeared, for a time, to throw discredit 

 on the value of evidence from vascular anatomy but stimulated dis- 

 cussion of the basic anatomy of floral organs and contributed in this 

 way to a knowledge of flower morphology. 



The Peltate Carpel. The theory that the carpel is basically a peltate 

 organ arose from similarities seen between the carpel and the peltate 

 leaf and has received much attention in continental Europe since 1925. 

 Under this theory, the carpels and gynoecia of many taxa have been 

 reinterpreted, with support from details of ontogeny and anatomy. 

 Peltate, in the sense of shield-shaped, as commonly used in leaf descrip- 

 tion, is an unfortunate term for use in this theory; the adjectives ascidi- 

 form, tubular, and utricular, which have been used less frequently, 

 much better describe the form of the carpel. The peltate theory presents 

 a morphological origin for the carpel more complex than the simple fold- 

 ing or inrolling of the margins of the lamina. Peltate form in the carpel 

 is assumed to have arisen by the turning upward (ventrally) of the 

 basal lobes of the lamina and their fusion, margin to margin, as in the 

 formation of peltate leaves. Where tlie two marginal meristems meet, 

 they unite, forming a transverse meristem, the cross zone. As the pri- 

 mordium elongates, the cross zone, continuous with the marginal meri- 

 stems, is said to build up a ventral strip of carpel wall, which, united 

 with the lateral walls, forms a tubular organ. Under this theory, the 

 ovules are borne on the wall formed by the cross zone. The cross zone 

 is considered a region of much morphological and functional significance. 

 Its presence or absence, its position, and its degree of fertility — number 

 of ovules borne — are seen to give much information concerning the 

 evolution of the carpel. 



Carpels are described as peltate or epeltate (not peltate). Peltate 

 carpels have great variety of form, variety that is said to depend chiefly 

 on the extent of the activity of the cross zone, as seen in the length of 

 the carpel stipe and of the part of the carpel below the cross zone. 



Two types of peltate carpels are described: manifest peltate, with 

 well-defined stalks and a tubular lamina that has been formed by a 

 well-marked cross zone; latent peltate, intermediate between manifest 

 peltate and epeltate, with a very short tubular base and the cross zone 

 only "suggested," or present only in early ontogeny. Achene types, such 

 as the carpels of Thalictnim, are cited as the best examples of the mani- 

 fest peltate type. Forms intermediate between achenes and follicles, 

 such as those of Calycanthus and many genera of the Rosaceae and 

 Ranunculaceae, are given as examples of latent peltate carpels. The 

 "primitive achene" of Ranunculus, described as having a solitary ovule 

 on a "latent" cross zone, is considered to represent a "first stage" in the 



