ORGANS OF REPRODTJCTION. 353 



many other Caryophyllaceous Plants, exhibit a little scale on 

 their inner surface at the point where the limb of the petal is 

 united to the claw. A somewhat similar scale, althoiigh less 

 developed, occurs at the base of the petals of some species of Ba- 

 HunciUus {fig. 482). The formation of these scales is supposed 

 by many to be due to the chorisis or unlining of an inner por- 

 tion of the petal from the outer. Other botanists consider these 

 appendages as deformed glands. Each petal of Parnassia {fig. 

 483) has at its base a petal-like appendage divided into a num- 

 ber of parts, somewhat resembling sterile stamens ; this is also 

 stated to be produced by transverse chorisis. 



In the natural orders Rhamnacese {fig. 774), Byttneriacese, 

 «Scc., the stamens are opposite to the petals, hence they are sup- 

 posed by many botanists to be produced by chorisis from the 

 corolla; others, however, explain this opposition of parts by 

 supposing the suppression of an intermediate whorl (see p. 355). 

 Transverse chorisis is also frequently to be found in the andrce- 

 cium, but it is less frequent in the gyncecium. Examples of 

 chorisis in the gyncecium are furnished, however, by Sedum {fig. 

 566), and Crassic/a {fig. 766), where each carpel has at its base 

 on the outside a little greenish scale, which is supposed by some 

 to be due to it. 



It will be observed, that in all the above cases. of transverse 

 chorisis, the parts which are produced do not resemble those 

 from which they arose, and this appears to be a universal law 

 in this form of chorisis. 



Collateral chorisis. — AVe have a good example of this form in 

 the Stock, Wallflower, and other plants of the natural order 

 Cruciferse. In these flowers, the two floral envelopes are each 

 composed of four organs alternating with each other {fig. 775). 

 Within these we find six stamens instead of four, as should be 

 the case in a symmetrical flower ; of these two are placed oppo- 

 site to the lateral sepals and alternate with the adjacent petals, 

 while the other four are placed in pairs opposite the anterior and 

 posterior sepals ; we have here, therefore, four stamens instead of 

 two, which results from the collateral chorisis of those two. In 

 some Cruciferse, as Streptanthus {fig. 776), we have a strong con- 

 firmation of this view presented to us in the fact that, in place 

 of the two stamens, as commonly observed, we have a single fila- 

 ment forked at the top, and each division bearing an anther, 

 which would seem to arise from the process of chorisis being ar- 

 rested in its progress. The flowers of the Fumitory are also 

 generally considered to afford another example of collateral 

 chorisis. In these we have two sepals {fig. 777), four 

 petals in two rows, and six stamens, two of which are perfect, 

 and four more or less imperfect ; the latter are said to arise 

 from collateral chorisis, one stamen here being divided into 

 three parts. Other examples of this form are by some con- 



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