220 
parenchyma cells containing a few chlorophyll grains. Then fol- 
lows a plate like double layer of vascular tissue merging at 
the margins into parenchyma. The upper layer is composed of 
rather transparent and elongated cells, the under layer of short 
thick pitted tracheides merging on the under surface into the 
lowest layer of parenchyma cells with pitted or reticulate walls. 
At the margins of the disc the upper and lower parenchyma 
layers may separate forming a lenticular air space. The forma- 
tion of these discs is interesting, as being a case in which a 
morphologically radial but physiologically bilateral organ is sti- 
mulated by contact to form an organ, which is both physiolo- 
gically and morphologically markedly bilateral. 
The tendrils coil if attached to a glass rod, but more slowly 
than when in contact with a rough support, whilst the thickening 
is not so marked and no adhesive discs are formed. Thus: 
After 2 weeks. (1) on glass rod. diam. = 85, (2) coiled around loose string =95,(3) Free =68. 
(2) All 3 tendrils twining round rough stem. (1) diam. 190, small disc, (2) and 
After (3) 180 and 165, no discs. 
1 (8). ae Round glass rod, strong pressure, diam. 160, (2) on rough stem, 250, 
(3) unattached. 105. 
| All 3 segments inside a narrow glass tube, (1). 90, (2) 89, (3) 15. 
(d). 1 and 2, twining a 1 glass rod, (1) . 115, (2) . 120, (3) unattached = 65. 
Month. 
The tendrils of other members of the Bignoniaceae shew inte- 
resting resemblances to, and connections with, the irritable hooks 
of hook climbers, as well as affording a series of interesting 
transition forms. Thus in B. albolutea and B. speciosa the tendrils 
are thin simple, unbranched and highly irritable, belonging 
the Passiflora type. In B. Jittoralis the tendril is divided into 
a basal peduncular portion, in which only slight irritability 
present, and a shorter terminal portion, which is trifid ant 
which in some plants of this type may branch again. Amplt- 
lobium mutisii also has tendrils with trifid extremities and the 
apices of these may, when in contact, form adhesive sucker i 
discs. Finally, in B. unguis and Nyctocalos Thomsonae the trifid 
extremity of the short tendril bears three short, rather thick 
and stiff, straight or slightly curved claws with recurved shatP 
pointed extremities. To the description given by Darwin (1. i 
p. 67) of the irritability and mode of action of the claws # 
