ANGIOSPERMS. ^^8 j 



the absent organ does not disappear in the course of development, but never comes 

 into existence at all, if the hypothesis of the suppression of the part is confirmed 

 by a comparison of the relationships of number and position in nearly-allied plants 

 The hypothesis of an abortion of this kind was, however, for the first time placed 

 on a firm basis by the theory of descent. 



The number of stamens in a flower is only rarely so few as one or two ; it is 

 usually larger, and equal in number to that of the perianth-leaves, and they are 

 then arranged in the form of rosettes, either spirally or in whorls. If the arrange- 

 ment of the perianth-leaves is spiral, that of the stamens is usually the same, and 

 the number of the latter is then very commonly large and indefinite, as in Nymphaea, 

 MagnoHa, Ranunculus, Helleborus, &c. ; but in this case they are sometimes also 

 few in number and definite. 



IMuch more often, however, the stamens are arranged in one or more whorls, 

 those in one whorl being then usually equal in number and alternate with those in 

 the other whorls, and with the perianth-leaves [symmetrical flowers of English text- 

 books]. There are, however, numerous deviations from this rule [unsymmetrical 

 flowers of English text-books] occasioned frequently by the abortion of particular 

 members or of whole whorls, or by their multiplcation, or by the superposition of 

 consecutive whorls ; and not unfrequently in the place of a single stamen two or 

 even more will arise side by side [dedoublemcnt). These phenomena, which are 

 often difficult to make out, are nevertheless of great value in the determination of 

 natural affinities, and will be still further examined in the sequel. 



Dei'clopmenl of the Pollen a?id of the Anther-walP. The description given in 

 this place will apply only to the ordinary cases in which the pollen is formed in 

 separate grains in the four loculi of the anther, and falls out of the anther after it 

 has opened ; some of the more important exceptions will be mentioned hereafter. 



Immediately after the perianth-leaves, or their innermost whorl, first become 

 visible on the receptacle as roundish protuberances, the rudiments of the stamens 

 make their appearance in a similar manner, but usually obtain a considerable start 

 in growth of the corolla, which not unfrequently remains for a considerable 

 time in a very rudimentary condition. The form of the stamen, which consists of 

 homogeneous primary meristem, very soon shows the outlines of the two anther- 

 lobes united by the connective; the filament is still very short, subsequently it 

 also grows slowly, and it is only just before the expansion of the flower that it 

 elongates very rapidly by vigorous intercalary growth. When the four pollen-sacs 

 make their appearance externally on the young anthers as longitudinal protuberances, 

 a layer of cells becomes difl"erentiated in the direction of their length^, through 



* Nageli, Zur Entwickelungsgeschichte des Pollens ; Zurich 1842.— Hofmeister, Neue Beitnlge 

 zur Kenntniss der Embryobildung der Phanerogamen, II. Monocotyledoiien. 



M am indebted to a letter from Dr. Warming for the following account of the first origin of 

 the mother-cells of the pollen :— ' The mother-cells of the pollen originate by the division of the cells 

 of the outermost or sub-epidermal layer of the periblem from one to three times by tangential walls, 

 the outermost of the cells which are thus formed being also divided by radial walls. In those 

 plants which have been more minutely examined (Hyoscyamus, Datura, Cyclanthera, Euphorbia) 

 the innermost layer of these cells becomes immediately converted into the primary mother-cells of 

 the pollen, the inner of the layers which lie between them and the epidermis becoming absorbed, 



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