ON THE ANATOMY OF MAGNOLIACE^. ]19 



thin uiiliiiiiified walls. Each group siirroniuls the first -formed spiral 

 vessels and is destined to he liunitied in the course of time. Primary 

 medullary rays usually consist of tw(^ or three radial rows of cells ; 

 hesides these there are found numerous small rays consisting of a 

 single row of cells. 



The ])ith C(^mmonly consists of cells with thick, lignified, ])itted 

 walls, hut sometimes there remains in the central portion (^f the pith a 

 grou]) of cells with urdignified walls. 



Petiole. — On the epidermis a few hairs are sometimes present. 

 They especially grow in the groove whicli runs longitudinally along 

 the u])per surface of tlie petiole. The hy])oderma is present. Tlie 

 (il)i-o-vascular hundles form a ring enclosing the pith. Sclerenchy- 

 matous fihres are well develo])ed and constitute a continuous sheath 

 around the bundles ; they are unlignified in the basal portion of the 

 petiole. The phloem ])ortion is here and there crossed by the 

 medullary rays, and the portion of the ray which bridges the ])hloëm 

 is made u\) of scleroblasts. unlike that of the stem the pith is formed 

 of thin-walled parenchyma. 



B](t(h'. — Its structure is generally com])act. The stomata do not 

 ])resent any peculiai-itv. Hairs grow on the midrib and their base is 

 often made up of several cells. The cuticle of the midrib forms 

 a number of longitudinal ridges, which j)resent in a cross section 

 cuticular indentations (PI. II, Fig. 3). Directly under the e])idermis 

 of the lower side of the blade there is found a layer of cells 

 which forms the hypoderma. The ai-rangement of the fibro-vascular 

 bundles of the midrib is not completely circular, but shows a 

 discontinuous portion turned towards the u[)per surface of the blade. 

 Aofg'reo-ates of crystals ave also met with in the cells of the cortical 

 portion of the midrib. 



Pool. — In the older root the o-eneral structure does not differ 



