STRUCTURE OF SEEDS 7 



subject of various important memoirs, which, however, have 

 been almost exclusively descriptive. Dalmer J indeed quotes 

 Schleiden, who, speaking of Berberis, pointed out that among 

 the normal anatropous ovules here and there one occurs which 

 is orthotropous, and that these never develop into seeds (' Die 

 Befruchtung cler Ovule scheint mir aber in ganz bestimmter 

 Beziehung zu dem vorgeschriebenen Lauf der Pollenschlauche 

 zu stehen, denn stets beobachtete ich, dass diese regelwidrige 

 atropen Eichen unbefruchtet blieben '). The pollen-tubes, 

 however, would naturally follow the regular course ; and we 

 could not, I think, deduce a general conclusion from such rare 

 and abnormal cases. Dalmer himself does not seem to have 

 done so ; for, after referring to the different forms of ovules, 

 he observes that ' sometimes the form of the ovule appears to 

 be adapted so as to facilitate the entrance of the pollen-tube ' 

 (' scheint zuweilen die Gestalt des Ovulums dem Eintritt des 

 Pollenschlauches angepasst zu sein '). Even here, then, the 

 explanation I venture to suggest seems referred to rather as 

 an exceptional occurrence than as a general explanation of 

 this remarkable arrangement. It must be admitted that there 

 are some cases in which the anatropy of the ovule appears at 

 first sight rather disadvantageous than otherwise. Most of 

 these can, I believe, be explained, while in some it is possible 

 that the plants retain, even perhaps to their present disad- 

 vantage, an arrangement inherited from an ancestral condition 

 in which it was beneficial. I hope, however, to enter into this 

 question more fully on a future occasion. 



The mature seed contains the more or less differentiated 

 embryo, in some cases, as in Larkspur (Delphinium) (fig. 104), 

 very small, consisting only of a small basal portion the radicle, 

 which on germination gives rise to the primary root, and one 

 (Monocotyledons), two (Dicotyledons), or several (Conifers) 

 seed-leaves or cotyledons, sheathing a microscopic plumule 

 from which the future stem is developed. The rest of the 

 space is occupied by the mealy, oily, fleshy, or horny endo- 

 sperm. In other cases, as in the Ash (Fraxinus) (fig. 46) or 

 Castor Oil (Ricinus) (fig. 52), the embryo is much larger, and 



1 ' Ueber die Leitung der Pollenschlauche bei den Angiospermen,' Jenaisch 

 Zeits. 1880, p. 530. 



