92 SUMMARY OF CURRENT RESEARCHES RELATING TO 



ment in the rliizome, when those of the stem are collateral ; the pre- 

 dominant character of the vessels is pitted in the former, spiral and 

 reticulate in the latter. As a general resume, the storing-tissue and 

 suberous tissues are usually strongly developed in the rhizome, while 

 the assimilating tissue is wanting, and the mechanical tissue is 

 greatly reduced. While the rhizome retains all the essential anato- 

 mical characters of the stem, it yet shows some approximation in many 

 ways to tlie structure of the root. 



Anatomical Structure of the Stem and of TTiidergroiind Stolons.* 



According to Herr F. Haupt, the outer walls of the epidermal cells 

 of stolons are thicker than those of stems, although less cuticularized ; 

 the lateral and inner walls are also thicker. The stomata are less 

 numerous in stolons ; when beneath the soil they are usually larger. 

 Stolons have, as a rule, no trichomes ; hairs occur in Labiatse and 

 in the potato, but are more delicate, and are composed of a 

 smaller number of cells ; glandular hairs are found on the stolons of 

 Labiataa. Cork occurs in both organs. The inner endoderm is usually 

 more strongly developed in stolons. In the vascular bundles the 

 xylem is always reduced in the stolons, and the phloem, on the other 

 hand, increased. The mechanical tissues, including coUenchyma, 

 Bclerenchyma, and the interfascicular tissue, are always reduced in 

 stolons. Starch usually occurs abundantly in stolons, especially in 

 those which persist through the winter. 



Anatomy of the Stem of Cruciferse.j — Herr E. Dennert classes 

 the Cruciferee under seven different types, dependent on the arrange- 

 ment of the tissues, and especially on the nature of the " strengthen- 

 ing-ring " which incloses the vascular bundle, composed of primary 

 prosenchyma, or of inner cambium and inner bast, or of all these 

 elements, viz. : — 



1. Auhrietia-tj-pe. The prosenchyma is wanting in the strengthen- 

 ing-ring ; the bast-fibres unite into a ring. 



2. Teesdalia-tj])e. The hard-bast and primary prosenchyma unite 

 into a continuous ring, with which the separate bundles are in 

 apposition internally. 



3. CocMearia-tjTpe. The ring consists of alternate groups of 

 vessels and bridges of primary prosenchyma ; it undergoes very 

 little or no change in the isolated cambium-strings. 



4. Sisymbrium- Alliaria type. The ring is much stronger ; but the 

 cambium-strings remain isolated. 



5. Turritis-tj])e. The continuous cambium produces no medul- 

 lary rays. 



6. Brassica-tjjye. When the cambium has become continuous, it 

 produces radiate prosenchyma in addition to vessels and secondary 

 prosenchyma. 



7. Bajyhanus-tj-pe. The individual bundles are separated by 

 primary medullary rays ; secondary rays also appear later. 



* Ber. Bot. Sallsk. Stockholm, Dec. 27, 1884. See Bot. Centralbl., xxiii. 

 (1885) p. 234. 



t Dennert, E., ' Beitr. zur vergleich. Anal, des Laubstengels der Cruciferen.' 

 37 pp. (1 pi-), Marburg, 1884. 



