i8o SIGNIFICANCE OF MALFORMATIONS IN ORGANOGRAPHY 



develop. This kind of case has been abundantly used with a view to 

 obtain a decision regarding the ' morphological nature ' of the stamen, 

 an endeavour utterly futile as these malformations are obviously dis- 

 turbances of the normal development provoked by disease. The more 

 the normal development is disturbed the easier is it for the sporangia 

 to be replaced by vegetative organs. There is no transformation of the 

 former into the latter, and intermediate stages between the normal and 

 the abnormal conditions do not prove such a transformation, they only 

 show that the disturbance can begin at different stages of development. 

 The morphological significance of the stamen is determined by its 

 developmental history and by comparison with the Pteridophyta, and 

 by these means we learn that the stamen is a sporophyll which like 

 other sporophylls has arisen by the transformation of a primordium of 

 a foliage-leaf 1 . 



The most completely malformed stamens are those in which there 

 is no trace of formation of the pollen-sacs (sporangia) a case similar 

 to that of the phyllody of sporophylls of ferns 2 . The stamens then 

 appear either as foliage-leaves or as petals, the latter being the case 

 when the primordium of the stamen before the laying down of the pollen- 

 sacs is affected by the factors which cause the primordium of a foliage- 

 leaf to develop into a petal. In intermediate cases the pollen-sacs appear 

 more or less completely developed, but are usually distorted. Special 

 importance has been attached to those malformations of stamens in which 

 a ' four-winged ' leaf is developed, that is to say, a leaf in which two 

 lamellae spring along each side of the length of the midrib. But there 

 is no difficulty in explaining this appearance by reference to the normal 

 history of the stamen. A young stamen before the appearance of the 

 primordia of the spore-forming tissue is a four-angled body, and in each 

 of the angles the primordium of a sporangium, the archesporium, is 

 differentiated. In phyllody of a stamen each of the four angles grows out 

 as a small leaflet, a phenomenon of growth which is altogether abnormal 

 when compared with the usual condition, but which occasionally is found 

 in a similar way in vegetative leaves. No greater mistake can be made 

 than to consider each leaflet as the product of the transformation of 

 a pollen-sac, for these have not been formed or there is at most a very 

 reduced pollen-forming tissue. What has here taken on the form of 

 a foliage-leaf or part of a foliage-leaf is not the pollen-sac bnt a part of 

 the sporopkyll, and we have no more to deal with a reversion than we 

 have when the staminal primordium is transformed into a simple foliage- 

 leaf or into a petal. No useful purpose therefore would be served were 



1 Much of what follows I take from my ' Vergleichende Entwicklungsgeschichte der Pflanzenorgane, 1 

 as it is still applicable. 



2 See page 183. 



