6o2 



PHANEROGAMS, 



chosen for the various separate organs, in order to render the explanation more readily- 

 visible to the eye. The leaves of the perianth are represented by arcs of a circle, a kind 

 of mid-rib being indicated on each of the outer whorl of these, or calyx, merely in order 

 to distinguish them at a glance from the inner whorl. The sign chosen for the stamens 

 resembles a transverse section of an anther, but without reference to the position of the 

 pollen-sacs or of their mode of dehiscence whether inwardly or outwardly. When the 

 stamens are branched, this is indicated by the signs being grouped, as in Fig. 408, where 

 the five groups correspond to five branched staminal leaves. The gynaeceum is treated 

 as a simplified transverse section of the ovary, since it is thus most easily distinguished 

 from the other parts; the marks within the loculi of the ovary indicate the ovules, 

 which however are only represented in those cases where their actual position can be 

 expressed by so simple a plan. The size, form, and cohesion of the separate parts are 

 not taken into account at all. The construction of these diagrams is based partly on 

 careful investigations of my own, but chiefly on the studies of Payer in the history of 

 development (Organogenic de la fleur), as well as on the descriptions of other authors 

 (Doll, Eichler^, and Braun). 



I draw a distinction between empirical and theoretical diagrams. The empirical dia- 

 gram only represents the relative number and position of the parts, just as a careful 

 observation shows them in the flower ; but if the diagram also indicates the places 

 where members are suppressed — -which can only be determined by the history of 

 development and by comparison with allied species, especially if it points out relationships 



Fig. 406 —Diagram of the flower of 

 L iliacece. 



FIG. 407.— ^Diagram of the flowel- of 

 Celasiriis (after Payer). 



FJg. 408.'— Diagl-atn of the flower of 

 Hypericum calyctnum. 



which are entirely the result of theoretical considerations — I call it a theoretical diagram. 

 If the comparison of a number of diagrams shows that, although empirically diff'erent, 

 they nevertheless yield the same theoretical diagram, this common theoretical diagram 

 may be termed the type or typical diagram according to which they are all constructed. 

 I consider the careful determination of such types an important problem, the solution of 

 which may be extremely useful in the classification of Angiosperms. When the type has 

 once been ascertained, the theoretical diagrams which correspond to it may be treated 

 as derivative forms from which particular members have disappeared, or where they have 

 been replaced by a number of members. From the stand*point of the theory of descent 

 the type corresponds to a form still in existence or that has already disappeared, from 

 which the species to which the derivative diagrams belong have arisen by degeneration 

 {i. e. by abortion ^) or by multiplication of the parts. 



A few examples will explain this. The flower of Grasses, which is seated among the 

 paleae, .may be deduced, as is shown in Fig. 409, on the theory of the abortion of certain 



* [Eichler, Bliithendiagramme, I, II, 1875-8.] 



^ The construction of the diagram itself shows that the theory of abortion is justified even 

 where the earliest state of the flower-bud gives no indication of the absent member, if the number and 

 position of the parts present point distinctly to such a hypothesis. If the idea of abortion in this 

 sense is not admitted, neither can the increase in number of individual parts, or their replacement by 

 several, be allowed. It is only the theory of descent that gives a rational explanation of either fact, 

 and that a very clear one. 



