7(5 THE CADSES OF rmCOTATIOSS IB TDIIGISOEKCK
a , o oxcoutod b y th« loaves of « r i o » spccicB of p k n t s , wo find t h . t n d i s t i n d . ni
d i r e c t rotation is traooaWo between r a p i d i t y of moTement and • toxha-al f a c i h t i b for
n i t r a t i o n . In the case of Cassia aMa and C. » » « ( , • « » , the niovemonts, when a the.r
n , a r i n n u „ , aro v e r y extensive, bnt are i n v a r i a b l y slowly and g r a d u a l l y e a r n e d out, and
t l , e p u h W p a r ^ n i y m a is very dense and scantily p i t t e d ; m and
even more in i » » ™ j i « « » , the rata of movement is considerably increased and the
p e l v i n a r parenchyma, althongh nnprovided with a f d l y - d e v e l o p e d system of rnterceltalar
spaces, i i c o m p o L d of cells the walls of which are very abnnclanlly p r i e d , and m
L p ^ m a r y pÌlvini of M » » » F " « » movements a t t a i n a m — n raprdrty, and the
ssnes are not only most elaborately and extensively pitted, bat are provided wath a
vc hi°h y-developed system of mtcrceltalar spaces, aHording abnndant accommodatron
t o any flAlwhidi may escape f r o m the coll cavities in conse<inence of any mereased
i i l t r a t i o n.
CHAPTER X.
l i t e inobEmcnts of tlt£ fcabcs of #ltmos'd l-uiiira.
T h e cenerai appearance of the leaves of » » » « i « « " is,
t o e v e i ; on bat i f i s necessary to allude t o certain of their characters in somewha
d e t a W M i i o n , seeing t h a t these have a n iu.portant b e a r i n g on t h e r a p i d i t y with which
. b e y are capable of c x e c n t i n g movements u n d e r oertani conditions
T h e following data .vere obtained f r om a single, l a r g e , active leaf
... 0-56 ^ammes.
1. Weight of the entire leaf ... .•• •• ^
2 WeigU of the petiole ¡»oludius the primary put™»! - "
3. Weight of a . . s . c o . d . r r pnlvioi, s.eondary petioles .nd pian.des ,,
4. Length of primary pidvinue ••• ••
5 Thickness o£ primftry pulvinus ... •;• "
6, Lenstti of piim.ry petiole from the distal erfrem.ty ot the ppipnlvinm
to the points of origin of the proj.mal p m . of ^^^^
7 L r » g t i r f ^ t h r r . m . i " i n g portion of the p r i m » , petiole h e t « .n
the sites of origin ol the prorimd and distel pan. of second- ^^^^^^ ^^
ary pulvini ••• , . " ' "
8. Length ol the seconder, petioles, inelndin- t h . seconder, p n l v m i -
(«) Proximal p«ù - - - ^ "
(J) Diitel psir ... - - - "
9. Length oi seoond.iy p n l m i - - " "
JO. Thickness of secondary pulvini
11. Kumher of pinnules on secondary petioles— ^^
(a) Proximal pair ... •.• i 19
( 25
[i) Distal pair — ••• -^24
12 Area of laminar sm-face (determined by gumming down the
dotaelied pinnules on a sheet of paper, so as to form a con-
. . . ... ... 7 squero inches,
tmuoue stratum) . . ..
13. Number ^ 160,000 pe.squore inch.
(а) Supenor epidexnus ' I
(б) Inferior epidermis ... - '"onoaUrt
14 Number of stornata on entire laminar surface 3,920,000
IN THE MOTOR ORGAKS OP LEAVES. ' '
111 tho case of another leaf, of which careful weig-htments were m i d e , the results
were as f o l l o w :—
1. "Weight of entire leaf ... ... ... ••• 0-47 grammes.
2. Woiglit of primary petiole, including primary pulviuus ... 0'07 „
3. Woiglit of primary puWnua ... ... ... ... C Ol „
4. Weight of secondary pulvini, secondary petioles and pinnules ... 0"40 „
5. Weight of primary petiole without t}ie primary pulvinus ... 0'06 „
Tho most i m p o r t a n t points to be noted are, Jirsf, the great l e v e r a g e to which t h e prim
a r y p u h i n u s is exposed (vide Appendix A), and, second, the excessive t r a n s p i r a t o ry
f a c i l i t i e s which are provided b y the laminar surfaces. Taking the d a t a derived f i o n i tho
sccoud leaf in which the weight of the p r i m a r y pulvinus was determined, it appears
t h a t tho pulvinus had t o support a weight forty-six times as great as its own, and of
w h i c h 85 per cent, was s i t u a t e d at the distal e x t r e m i t y of an elongated rigid lever,
r e p r e s e n t e d by the p r i m a r y petiole. The power in this lever system is applied at tho
immediate neighboui'hood of the fulcrum, and t h e weight is situated at the end of a
l o n g lever—conditions i m p l y i n g extreme i n s t a b i l i t y of equilibrium in event of any
fluctuations in the power. The excess of t r a n s p i r a t o r y facilities furnished by the
l a m i n a r surfaces is m a i n l y due to the fact that both the inferior and superior epidermis
a r e provided with stomata (Plate V, Figs. 9, 10). The numbers of stomata on tho
i n f e r i o r epidei-mis are not in excess, but rather fall short, of those present on the
i n f e r i o r surface of the pinnules of Pitkecolohium saman-, but in the latter, as well
as in the other nycfitropie leaves which have been specially considered liere, tiie
superior epidermis is e n t i r e l y wanting i n them. Additional facilities for the occurrence
of active t r a n s p i r a t o r y loss are, moreover, provided by t h e e x t r e m e l y open character of tlie
p a r e n c h y m a i n t e r v e n i n g between the pallisade cells and the inferior epidermis (Plate V,
F i g . 11). There are thus stmctural grounds for assuming that veiy active transp
i r a t o r y loss of fluid must occur under favourable circumstances, and that such loss
a c t u a l l y takes place is d e m o n s t r a t e d by the following experimental d a t a :—
Experiment I.—A pot-plant of Mimosa pudica bearing seven leaves was t a k e n . The
hole in the b o t t om of t h e pot waa f i r m l y corked, and the entire outer surface and lip
were t h i c k l y coated with m e l t e d wax. A glass plate, l a r g e enough to cover t h e mouth,
was t h e n divided into two halves, and a small piece was filed out i n the centre line of
division, so t h a t when the halves were a d j u s t e d to one another t h e y f o i i n e d a plate with
a small central perforation. These were next luted down with molted wax over the
mouth of the pot, so t h a t the lower part of tho axis of the p'ant passed t h r o u g h the
c e n t r a l opening and, finally, the line of division and the opening were also carefully
l u t e d . The pot was n e s t placed in an hermetically-closed chamber containing a vessel
t h e weight of which had been determined, and which contained 60 grammes of pure
sulphuric acid, and tho whole apparatus was set in the open air in d i f f u s e d sunlight.
The leaves remained in a stato of extreme expansion and olevHtina. At t h e close of four
hours the sulphuric acid was removed and weighed, and the weight amounted to 51-f>
grammes, i n d i c a t i n g an absorplion of 1'6 grammes of water of t r a n s p i r a t i o n . Tho acid
was now r e t u r n e d to the chamber, and the latter anew hermetically sealed, and on tho
f o l l o w i n g d a y it Avcighed 54-1 gi-ammes, corresponding to an absorption of i-lc.c. of
water d u r i n g the period of t w e n t y - f o u r hours. The cover of the pot was now removed