574 PHANEROGAMS. 



own observations on Chenopodiaceae and Polygonaceae, but they also warrant 

 the assumption that the ovules previously described by Payer as terminal are 

 really so. Since, however, it is not my object here to enter into a detailed proof 

 of theoretical matters, it will be sufficient for the present to summarise the various 

 phenomena. 



With respect to position, the following classes may first of all be distinguished: — 



A. Ovules produced on the Carpels and springing from the carpellary leaves ; 

 and either 



1. Marginal, from the reflexed margins of the carpels (Figs. 385, 386, 



387, 390) ; or, 



2. Superficial, from the whole of the inner surface of the reflexed halves 

 of carpellary leaves, always apparently with the exception of the 

 mid-rib of the carpellary'leaf (Fig. 357, 382). 



3. Axillary or basal, arising from the base of the upper surface of the 



carpel or in the axil of the carpel {Ranuticulus, Seduui, ZanichelHa 

 according to Warming^). 



' See Warming, Rech. sur la ramification des Phanerogames, Kopenhagen i''72, p 22. Tab. XI, 

 fig. I -TO. Axillary ovules are no more to be regarded as buds (caulomes) than are the axillary 

 sporangia of Lycopoditim. 



[The question of the morphological significance of the placenta and of the ovule is one which 

 has been much discussed of late. With regard to the placenta, Schleiden, starting with the concep- 

 tion of the ovule as being a bud, considered the placenta to be necessarily an axial structure, 

 inasmuch as only axial structures normally bear buds (Princip'es of Scientific Botany. 1849, 

 pp. 382 ff.), a view which was adopted and developed more especially by French botanists (see 

 Payer, Organogenic). According to a second view, the placenta is a portion of the carpel itself, 

 usually of its margin, that is, that it is always borne by a leaf. This view has been revived of late 

 years by Van Tieghem (Rech. sur la structure du pistil, 1871), by Celakovsky (Ueb. Placenten und 

 Hemmungsbildungen der Carpelle, Sitzber. der k bohm. Ges., Prag, 1875 ; Vergl. Darstellung der 

 Placenten, ihid. 1876), by Braun (Bemerk. ueb. Placentenbildung, Sitzber. d bot. Ver. d. prov. Brand. 

 1874), and Eichler (Bliithendiagramme, II. 1878) has now accepted it. In spite of all that has been 

 written in support of these two theories, it cannot be admitted that either of them satisfactorily 

 explains every possible case : if the former must evidently be forced when it is applied to a case of 

 parietal placentation, this is equally the case with the latter when it is applied to free-central placen- 

 tation, as in the Primulacese. Both these attempts at generalisation seem to be too arbitrary. In 

 consequence a third view has been promulgated, more especially by Huisgen (Untersuch. ueb. die 

 Entwickelung der Placenten, Bonn 1873) and formerly held by Eichler (Bliithendiagramme, I. 1875), 

 that the nature of the placenta is not the same in all ca.es. In the Primulacese, for instance, it 

 belongs to the floral axis, and, according to Huisgen, this is also the case in certain instances of 

 axile placentation, as in the Solanaceae. Lobeliacese, Ericaceae, Malvaceae, and Hypericaceae, the 

 placenta in these orders being a prolongation of the stem ; it also belongs to the axis in such forms 

 as the Piperaceae, in so far as any placenta can be said to exist in them at all : in the Violace^ and 

 Leguminosse and in Monocotyledons the placenta is a development of the carpels : finally, in Ciuci- 

 ferae and Resedaceae, and, according to Barcianu, in the Onagraceae (Ueb, die Bliithenbildung der 

 Onagraceen, Schenk's Mittheilungen, II. 1875), the placenta is an independent organ, probably a 

 phyllome, a view which was held by Treviranus (Physiologic, II, 1838). 



Now with regard to the ovule. Schleiden, Braun, and most of the older botanists regarded 

 the ovule as being a bud, but many regarded it as a leaf or part of a leaf (for the early history of the 

 subject see Braun, Polyembryonie und Keimung von Ccelehogyne, i860), a view which, as stated 

 above in the text, has been more recently revived by Cramer ; this view has been further developed 

 by Celakovsky (Ueb. die morphol. Bedeutung der Samenknospen, Flora, 1874; Zur Discussion 

 ueber das Eichen, Bot. Zeitg. 1875, and Vergriinungsgeschichte der Eichen von Alliaria officinalis, 

 ibid. 1875, und von Trifolinm repens, ibid. 1877), and so far modified that, according to him, the 



