52 ANATOMICAL STKUCTUKE OF THE OLIVE. 



strand has no support of stereome in the stricter sense of the word, 

 but is simply surrounded by a small collenchymatic tissue. Lep- 

 tome and hadrome show the same structure as in the midrib of the 

 blade. 



The arrangement of the tissues of the stem is shown in Plate V, 

 figure 2. The cross section of the young twig is quadrangular and 

 /minutely four winged. The thin, smooth cuticle covers an epidermis 

 with hairs similar to those of the leaf, and the outer cell walls are 

 very thick; inside the epidermis are about twelve layers of cortical 

 parenchyma, collenchymatic in the peripheral layers but more thin 

 walled around the stele. Phellogen appears in the outermost layer 

 of the cortex and soon develops several layers of cork, of which about 

 three develop during the first summer. (Fig. 20.) 



There is no endodermis, but a stereomatic and very thick-walled 

 pericycle surrounds the stele. This pericycle, however, is not con- 

 tinuous, but consists of many strands of 

 stereome separated by a few parenchy- 

 matic cells. The leptome presents a 

 circular zone bordering on the pericycle, 

 and is separated by cambium from the 

 ^ ^^ hadrome. The vessels (the scalariform 



^oOdor^^O^P^ ones especially) are thick walled and 



"^Ooo^j-^^^QO ^°"' separated from each other by paren- 

 ^ ^'^^-^ ^--^ chymatic rays, each of a single row of 



Fig. 20.-Development of cork layers in rather tllin-Wallcd Cclls. The Cells of 

 thecortexof an olive stem. (X 150.) 



the pith (which is solid) have thick 

 porous walls and contain much starch. 



As compared with the preceding (the Mission variety from Niles, 

 Cal.), the unknown variety of olive of which material was collected 

 in the orchard at Phoenix, Ariz., is noteworthy for the extremely 

 thick-walled epidermis on both faces of the leaf; thick- walled collen- 

 chyma extending from the epidermis to the pericycle of the midrib; 

 more stereome in the pericycle; palisade and pneumatic tissues more 

 compact but containing less stereome. In the petiole all the tissues 

 are extremely thick walled. Cork develops very early in the stem, 

 since even in the apical internode there are seven layers. The epi- 

 dermis of the apical internode is extremely thick walled. 



The two unidentified varieties collected in the abandoned orchard 

 at Palm Springs appear to be identical in anatomical structure. 

 From the variety growing at Phoenix they differ only in the much 

 narrower midrib. 



192 



