GREENFIELD: HISTOLOGY OF THE RUSSIAN THISTLE. 271 



cicatricosicm Sond., Stylidiuin dichotomum, D. C, Stylidiuin fruticosum 

 R. Br., Stylidium lancifolium, Stylidiimi rhynchocarpuni Sond. This ring 

 is due to the activity of a secondary meristem appearing in the pericycle 

 immediately below the endodermis (Van Tieghem, 1883-"84). The anom- 

 aly occurs in the roots of these also, and in the root but not the stem 

 of Stylidium graminifolium and S. spimdosum Van Tieghem (1878). 



Plumbaginace^. 



In Acantholinto)i the appearance of successive rings of growth is 

 combined with the occurrence of the medullary vascular bundles. It 

 has not been determined whether the secondary ring of bundles arises 

 in the pericycle or in the bast portion of the primary vascular ring. 

 In the genus .^gialitis the cross section appears similar to the cross 

 section of the genus Acantholinwn, but the meristem is from the layer 

 of cells immediately outside the sclerenchymatous bands (Solereder, 

 1908). 



Primulace^. 



In the group Officinales and in the Auriculas a system of vascular 

 bundles is formed in the pericycle of the root stock. 



CONVOLVULACE^. 



A vascular bundle ring appears in Argyreia, Calonyction, Iponioea, 

 Maripa, Merremia, Parana, and Rivea. The ring is due to the activity 

 of a secondary meristem which arises on the outer margin of the primary 

 phloem and internally to the bast fibers of the pericycle. 



BlGNONIACE^. 



A secondary zone of growth appears in the cortex of Callichlamys 

 Miq., Glaziovia Bureau, and Haplolophium Cham. 



Verbenace^. 

 In the genus Avicennia successive rings of growth appear, all extra- 

 fascicular in origin. 



PHYTOLACCACE.E. 



Some of the genera belonging to the tribes Rivinese and Euphyto- 

 lacceae are distinguished by having an anomalous stem structure which 

 consists in the appearance of successive rings of vascular bundles in the 

 pericycle. This anomaly also occurs in some species of Phytolacca, also 

 in Ercilla volubilis (Kriiger, 1884), Seguieria floribunda Benth., S. longi- 

 folia Benth. (Solereder, 1908), and S. americana (Schulz). 



NYCTAGINACEiE. 

 Anomalous structure of the stem apparently occurs in all the woody 

 species, and is also found in a certain number of the herbaceous species. 

 It has been recorded by various authors (RegTiault, 1860; Unger, 1840; 

 Gronlund, 1872; Peterson, 1879-'80; DeBarry, 1877; Radlkofer, 1883; 

 Solereder, 188.5; H. Schenck, 1893; Houlbert, 1893) in numerous species 

 of the genera Mirabilis, Oxybapkus, Boerhavia, Bougainvillea, Pisonia, 

 Eggersia, Phseoptillon, Neea, Leucaster, and Cryptocarpiis. The second- 

 ary meristem develops in the parenchymatous pericycle. 



