250 PRACTICAL BOTANY 



fan-shaped masses of secondary xylem will have joined 

 laterally, so as to form a complete ring. Annual rings 

 may also be seen in fact, the structure at the periphery 

 of ( the root now closely resembles that of the stem after 

 it has undergone secondary thickening. 



The root of Taxus differs in certain details of structure from 

 that of Pinus, and as it is typical of the majority of Gymno- 

 sperms, and is an excellent type for illustrating the process of 

 secondary growth in thickness, it will be well to make prepar- 

 ations from it also : the specimens are to be dug up carefully, 

 and washed to remove the soil. Selecting a young fibril of 

 succulent appearance, cut transverse sections at a point not far 

 removed from the smooth apex : treat with " eau de javelle " or 

 potash, wash with water, and mount in glycerine. Examine 

 under a lower power, and observe 



1. The piliferous layer, not clearly denned, while numerous 

 superficial cells have grown out as root-hairs. 



2. The broad band of cortex : note especially the well-marked 

 layer of cells, next outside the endodermis, with a peculiar 

 thickening of the radial walls ; sometimes the thickening extends 

 to cells of the next outer layer, and in some other Conifers (e.g. 

 Cupressus) it may be found to extend over several layers. 



3. The endodermis, which lies immediately within this layer, 

 and consists of cells with thin brown walls, and with the usual 

 dark clot on the radial cell-walls. Within this is the vascular 

 cylinder, which consists of 



4. The diarch, primary xylem, of which the two originally 

 distinct groups join at the centre to form a diametral plate. 



5. The two masses of primary phloem, on either side of this, 

 are not well marked. 



6. Between the vascular tissues and the endodermis is a 

 bulky pericycle, which usually consists of only a single layer 

 opposite the xylem, but it widens out into several layers opposite 

 the phloem. 



Cut transverse sections of an older part of the root : note in 

 these the cortex as before, or it may be turned brown, and be 



