Doyle — Some Researches in Experimental Morphology. 413 



1. The Structure and Variations of the Normal Petiole 0/ Pelargonium zonale 

 var. meteor. 



"While there are many references in the literature to the anatomy of the 

 order Greraniaoeae and even of Pelargonium [see, for example, Bruiiies (11), 

 and tlie literature cited in Solereder (12)], there is only one description of the 

 petiole of Pelargonium zonale. Jannicke (13) shortly says that it contains a 

 peripheral ring of bundles, some large and some small, which lie against a 

 comparatively weak mechanical ring (Bast ring). In the medulla there lies 

 free a central bundle. " Dasselbe besteht aus einer runden Cambiumgruppe, 

 die in ihrer Mitte eine kleine Bastgruppe und beiderseits im Diirchmesser 

 zweier grosserer Mestombiindel eine Grefassgruppe erzeugt, von denen die 

 eine starker ist wie die andere" (p. 18). 



Let us look now at Plate XXX, fig. 1. 



It is a photograph at 20 diameters of a normal, well-developed petiole 

 of Pelargonium zonale var. meteor. It is dorsiventral, [a) being the upper 

 side or the side turned towards the stalk, (h) the lower side. It is thus 

 flattened from above downwards. In fact, its greatest diameters are — 

 horizontally 3'6 ms. vertically, 2'7 mms. The peripheral ring of large and 

 small bundles as mentioned by Jannicke, appear clearly. One can see, too, 

 that at the middle of the upper side there is one large bundle with two 

 smaller ones closely approximated to it. Opposite them on the vertical 

 diameter of the petiole is another large bundle witli two small bundles on 

 each side. This appearance is quite constant in the variety, and will be of 

 importance in the subsequent pages. These bundles show nothing of im- 

 portance, consisting of primary wood and phloem. No tracheides are 

 developed, though traces of the primary cambium oau be seen in the large 

 bundles until the leaf is quite old. Its presence can be detected even when 

 the bundle gives every appearance of a complete cessation of cambial 

 activity. These bundles lie against a mechanical ring which is but poorly 

 seen, as at C. The nature of this ring — whether we are to refer to it 

 as sclerenchyma fibres, as Strasburger (14) would, or as bast used in 

 Haberlaudt's (15) sense, whether we are to regard it as developed from a 

 special tissue which we ordinarily call phloem, or with Morot (16) insist that 

 it is derived from an equally special tissue which we call the perieycle, 

 may indeed provide us interesting and important questions from the stand- 

 point of comparative anatomy, but need not detain us here. But very 

 definitely free in the medulla there lies the largest bundle of the petiole. It 

 is worthy of note that, contrary to Jannicke, the wood of this bundle is 

 obviously developed on one side only. It is equally worthy of note that, 



SCIENT. PEOC. K.D.S., VOL. XIV, NO. XXXHI. 3 X 



