194 SUMMARY OF CUEEBNT RESEARCHES RELATING TO 



Zamia floridana of producing new shoots and roots. It was stated that 

 portions of the stem not larger than a walnut had been *<.vn to produce 

 both root and shoot. In the stems studied, the new shoots generally 

 spring from the vascular part of the central cylinder, as many as five 

 shoots having been seen to spring from this region in a stem 3 cm. in 

 diameter. The vascular elements are continuous with the vascular 

 tissue of the central cylinder of the parent stem. Less frequently new 

 shoots arise from the peripheral part of the wounded surface of the 

 cortex ; both regions of origin may be used in the same stem. The 

 origin of the new roots is just as variable. In several cases they arise 

 from vascular tissue, but, as in the case of shoots, roots may arise from a 

 chip of the cortex of an old vein. The authors conclude that in the 

 case of the stem of Zamia the power of regeneration is present in all 

 nieristematic tissue ; in cases of mutilation the tissue chiefly concerned is 

 the phellogen of the callus, that over the region of the central cylinder 

 being more often successful than that over the cortex. 



Anatomy of Palm Roots.* — E. Drabble gives an account of his 

 researches on the anatomy of the roots of palms. More than sixty 

 species have been examined, and essentially similar results have been 

 obtained from each. The adventitious root has its origin in the peri- 

 cycle of the stem, arising as an extensive rhizogenic arc. The apex is 

 occupied by a non-stratified group of initial cells, which give rise by 

 division to a common ground-mass of parenchyma wherein, in very 

 young roots, appears a series of separate procambial strands. These are 

 continued, by secondary divisions of the parenchyma, into the central 

 cylinder of the stem. The strands, usually after undergoing repeated 

 bifurcations, are connected with the bundles of the stem. Each of these 

 strands gives rise to a " stele "-like structure with exarch protoxylem- 

 groups alternating with phloem-groups ; but without histologically 

 differentiated endodermis. As the root lengthens the procambial tissue 

 takes the form of a series of arcs by apical fusion of the strands. Still 

 later a lobed cylinder is produced, and finally the root-cylinder of a 

 monocotyledonous plant results. 



As a rule all the changes take place during the passage of the root 

 through the thick cortex at the base of the stem, but in several species 

 the lobed cylinder, or even the free strands, persist in the extra-cauline 

 portion. The internally directed protoxylem-groups usually die out 

 distally, but are occasionally represented by inversely orientated groups, 

 the metaxylem elements persisting as the large scattered vessels nearly 

 always present in palm-roots. The " medullary " strands are shown to 

 be in reality the reduced remains of some of the free basal " stele "-like 

 structures which have not entered into the composition of the vascular 

 ring. In some few cases, the proximally free strands unite to form not 

 a single cylinder, but three or more, so producing Cormack's " poly- 

 stelic " condition. Distally these become incomplete on the central Bur- 

 face, and give rise by lateral fusion in the apical region to first a lobed, 

 and finally a normal root cylinder. 



The author regards the" medulla " in palm-roots as merely that por- 



* Trans. I. inn. Soc., ser. 2 (Bot.) vi. pp. 427-00 (4 pis. nnd figs, in text). 



