ORIGIN OF ENDOGENS FROM EXOGENS. 495 



instance, of the Haloragece, is a good illustration. It has one 

 cotyledon which remains within the testa, as is so often the 

 case with endogens, the other being rudimentary. Ranunculus 

 Ficaria supplies another case. Though this plant is not now a 

 true aquatic plant, yet it flourishes vigorously by the waterside, 

 and has, I think, without doubt descended from an aquatic 

 plant. 



Irmisch * has given a description and plates illustrative of many 

 details of this plant ; and adds a feature w r hich I had not noticed, 

 particularly characteristic of endogens. The single cotyledon 

 when fully developed has a long sheathing petiole, forming a 

 closed tube at the base, excepting a small orifice, from which the 

 plumule can escape. It thus forms, as also occurs in Carum 

 Bulbocastanum, what Mirbel called a u coleoptile " in endogens. 



The peculiarities which seem to warrant the conclusion that 

 i?. Ficaria was originally an aquatic plant are the lacunae with 

 symmetrically arranged circumferential cells in the stems and 

 petioles, both having exceedingly lax parenchymatous tissue, and 

 the widely separated cords with deficiency of supportive tissue, 

 the cords becoming anastomosed at the nodes. The cordate form 

 of the leaf resembles that of other floating leaves of true aquatics . 

 The upper epidermis of the leaf is provided with stomata nearly 

 double in number those of the lower side, the chlorophyll being 

 pretty abundant in the cells of the lower epidermis, but very 

 sparing in those of the upper, that is, irrespective of the guard- 

 cells of the stomata. 



Lastly, it has one cotyledon, the other being suppressed. This 

 species does not seem to ripen its fruit often in England, but, 

 from some sent me which were apparently ripe, I found most of 

 the seeds to be only half developed, with no discoverable em- 

 bryos. In one, however, the endosperm was copious, but the 

 embryo had not advanced beyond the proembryonic condition. 

 Hegelmaier also describes and figures it in this condition f. On 

 the other hand, Irmisch figures it with a conduplicate cotyledon, 

 remaining within the endosperm during germination. Hence it 

 may be inferred that the cotyledon may exist in different degrees 

 of development, or rather of degradation, in this plant J. 



* 'Beitrage zur vergleichenden Morphologic der Pflanzen/ pis. i. & ii., 1854. 

 t ■ Vergieichende Untersuchuagea iiber Entwicklung dicotyledoner Keirne/ 

 Taf. i. fig. 25. 



X Op. cit. Taf. ii. fig3. 1, 2, (>, ic. 



LINN. JOURN. BOTANY, VOL. XXIX. 2 O 



