[40 



NA TURE 



\Jtme 7, 1883 



entrance of more dust from above. It is known that air in a 

 closed space will gradually free itself from dust, but the observa- 

 tion of a thin dust-free stratum at the top of the vessel is difficult. 

 If we conceive a vessel full of dusty air to be set into rapid rota- 

 tion, the dust might be expected to pass outwards in all direc- 

 tions from the axis, along which a dust free line would form 

 itself. I have tried this experiment, but looking along the axis 

 through the glass top of the vessel, I could see no sign of a dark 

 line, so long as the rotation was uniform. When, however, the 

 vessel was stopped, a column of comparatively smoke-free air 

 developed itself al >ng the axis. This I attributed to the forma- 

 tion of an inward flaw along the top of the vessel, combined with 

 a downward flow along the axis after the manner described and 

 explained by Prof. James Thom-on, so that the purified air had 

 been in intimate proximity with the solid cover. It would almost 

 seem as if this kind of contact was sufficient to purify the air 

 without the aid of centrifugal fo'ce. 



The experiments made hitherto in order to elucidate this ques- 

 tion have given no deciive result. If the thin convex blade 

 already spoken of be held in the smoke-box in a vertical instead 

 of in a horizontal plane, the lines of motion are much less curved, 

 and we might expect to eliminate the influence of centrifugal 

 force. I have not succeeded in this way in getting iil of the 

 dark plane; but since under the magnifier the curva'ure 1 f the 

 motion was still quite apparent, no absolute conclusi ill can be 

 drawn. 



ON THE MORPHOLOGY OF THE PITCHER 

 OF "CEPHAL07US FOLLICULARIS" 1 



""PHE brief, but most interesting, memoir on this subject read 

 -*- by Prof. Alexander Dickson before the Botanical Society 

 of Edinburgh on March 10, 1881, was the first to throw any 

 clear light upon the obscurity which had previously enveloped 

 it. The conclusions at which he arrived seemed to he fully sus- 

 tained by the facts which he then published ; but since there are 

 still botanists who do not fully accept those conclusions, any 

 independent evidence bearing upon the problem of the morpho- 

 logy of these curious pitchers may be worth recording. 



The publication of Prof. Dickson's memoir caused me to wa'ch 

 thegrov\thof my plants of Cephalotus with increa-ed interest. 

 From time to time abn rmal leaves have made their appearance, 

 which seemed to affjrd more or le^s support to the views wdiich 

 the Professor entert lined. This spring one of my plants has 

 developed a leaf the growth of which 1 have watched. When 

 this leaf first becime visible it bore no indication of being other 

 than an ordinary leaf of the plant, but its upper surface soon 

 exhibited a somewhat shrivelled appearance, like that of a leaf 

 distorted by the action of Aphides. It soon became evident 

 that this disturbance was but the commencement of the process of 

 pouching described by Prof. Dickson. That which at first ap- 

 peared t 1 be a mere distortion of the surface of the leaf soon 

 deepened into a considerable depression, which became more 

 considerable day by day until the leaf reached the condition 

 represented in my figures 1, 2, and 3. Fig. I represents the 

 upper, 2 the lateral, and 3 the inferior surface of this leaf. 



From the beginning of its growth a was the unmistakable, some- 

 what cuspidate apex of the leaf, as it was also the distal end of 

 the prominent ciliated ridge, b, the obvious precursor of the 

 middle d oral wing, wdiich forms so conspicu >us a feature of the 

 normal pitcher. It will be seen in Fig. 2 that this ridge only 

 extends downwards to the point c, whilst d was evidently the 

 fundus of the enlarging pouch, relations wdiich approximate 

 closely to what characterise these portions of the perfect pitcher. 

 On the under surface of the leaf (Fig. 3) we find this middle 

 wing extending downwards from <*, flanked on either side by a 

 smaller, slightly curved ridge, also ciliated, the two unquestion- 

 ably representing the lateral wings of the normal organism. It 

 is perfectly clear that the peripheral outlines of the figures I and 

 3 represent the true primary margins of the leaf from the point a 

 to the base of the petiole e. The upper half of this margin is 

 abundantly ciliated, the hairs becoming more scanty as we 

 approach the lower half of the leaf. 



Figs. 1 and 2 sh iw the form of what obviously represents the 

 lid,/, :>f the true pitcher. In its essential features it accords with 

 those figured by Prof. Dickson, who correctly recognised its true 

 homology. As in his Pig. 5, this lid is two-lobed, its central 

 indentati m, n. separating two triangular lobes. This arrange- 



• By W. C. Williamson, LL.D., F.R.S., Professor of Botany in the 

 Vict na University, Manchester. 



ment corresponds substantially with what exists in the normal 

 pitcher, only in the latter the lobes are large and rounded instead 

 of being small and triangular. The free margin of this rudi- 

 mentary lid is abundantly ciliated, as in the perfect pitchers. 



Thus far my specimen only confirms and illustrates the con- 

 clusions arrived at by Prof. Dickson, viz. that the pitcher is 

 merely a depression in the upper surface of the leaf, of which 

 the petiole e is identical morphologically with the terete petiole 

 of the true pitcher, whilst the lid, f, is an outgrowth of the 



Fig. 



Fig. 



upper surface of the leaf from the proximal margin of that 

 depression. 



Prof. Dickson was not able to decide with absolute certainty 

 which part of the matured normal pitcher represented the primary 

 apex of the leaf. In his abnormal specimens, as in mine, that 

 apex coincided with the apex a of the middle dorsal wing. As 

 is well known, in the perfect pitcher the entrance into the 

 pitcher is bounded by a thick, involuted, toothed rim, to which 

 the apical point of the dorsal wing is external. The Professor 



M 



1 1 .. 



was uncertain whether the apex a of the wing coincided with 

 the true apex of the leaf, or whether that apex is hidden in the 

 involuted margin of the pitcher. He inclines, however, towards 

 the former view, and I have the conviction that he is right. The 

 two ciliated margins, a' a', of Fig. 1, are obviously the two 

 lateral margins of the anterior portion of the normal leaf, de- 

 monstrating clearly that the point a is its apex. In the true pitcher 

 these margins have lost their ciliae, a few prominent teeth beinr 

 substituted for them, and become thickened at their inner side 



