60 ON SEEDLINGS 



the endosperm itself contributes also, 1 and hence a small 

 embryo is less liable to injury. 



SIZE OF COTYLEDONS. 



It is hardly necessary to say that the size of the plant does 

 not determine that of the cotyledons. Winkler has pointed 

 out that the largest of our Nettles has the smallest cotyledons. 2 

 It is, on the other hand, natural that large seeds, as a general 

 rule, produce large cotyledons. This is, however, by no means 

 a complete explanation. There are many cases in which the 

 cotyledons grow considerably after quitting the seed. In the 

 wonderful genus Welwitschia it was at one time supposed 

 that the two great leaves were persistent cotyledons. This 

 view is now abandoned. In many of the Monocotyledons, 

 however, the cotyledons acquire a considerable length. I have 

 already had occasion to allude to cases among the Dicotyledons 

 in which the cotyledon continues to grow for some time after 

 quitting the seed. 



Streptocarpus Eexii affords, perhaps, the most remarkable 

 case. The cotyledons are at first small, rotund, and shortly 

 petiolate. Soon, however, one of them begins to grow, and 

 becomes an at first ovate, then oblong, and finally panduri- 

 form, obtuse, entire, persistent leaf, 

 attaining a length of more than 

 18 inches. The other cotyledon 

 retains the original form, and soon 

 drops off. In some specimens, how- 

 ever, both cotyledons retain their 

 original form, and it is the first 

 true leaf which develops. 

 _ In the cultivated form of the 



FIQ. 105. Seedling of (Enothera ,-. 



bistorta, x8. Mango, the cotyledons are divided 



into more or less irregular lobes ; 



and in a specimen kindly given me by Mr. Eidley, one of the 

 lobes developed into an independent plant. 



1 See Marloth, 'Ueber Mech. Schutzmittel der Samen gegen schadliche 

 Einfliisse von Aussen,' Engler's Sol. Jahrb. 1883, p. 225. 



2 ' Ueber die Keimblatter der deutschen Dicotylen,' Verh. Bot. Ver. Branden- 

 burg, 1874, p. 11. 



