28 MERISTEMS 



ing- tissue is critically studied ^\ itli the aid of such vital stains as 

 "Neutral Red." Bailey (1930, p. 677) states: " Xormal ram- 

 bial initials are conspicuously vacuohited. Indeed certain of Ihcni 

 are as highly vacuolated as plant hairs, which are commonly cited 

 as illustrations of extreme specialization of the protoplast in fully 

 differentiated cells. The classical conception of non-vaeuolated 

 meristems. and the various physiological generalizations that have 

 been deduced therefrom should be abandoned." Just how the 

 form, Avail sti-ucture, vacuome, and peculiar methods of cytokine- 

 sis in cambial initials are related to the derivation in opposite 

 directions of such heterogeneous tissue syste7vs as i)hloem and 

 xylem is not yet clear. Tt would seem evident, however, that here, 

 as with comparable problems at the root ami shoot apex, experi- 

 mental studies (e.g., tissue cultures and transplantation) may 

 ultimately illuminate much of the o])scurity of this important 

 problem. 



The most instructive and realistic views of the vascular cam- 

 bium are secured from a study of living material whit-li may be 

 stained with neutral red (cf. Appendix, j). 142). With the aid 

 of a sharp, heavy knife and a sliding microtome, it is possible to 

 obtain useful tangential, radial, and transverse sections of the 

 cambium and its recent phloem and xylem dei-ivatives. The cam- 

 bium of Piniis is a good gymnospermous type with gi'eatly elon- 

 gated non-strati fie el fusiform initials while Rohiuia illustrates 

 a dicotyledonous type with shorter, rather evidently sfr<itifie<] 

 fusiform initials. 



IV. Suggested Drawings and Notes. — 



1. l'rei)are outline drawings of various availal)le types of 

 angiospei-mous and gymnospermous shoot apices. In each out- 

 line, indicate diagraiiunatically by means of legends, the jiosition 

 and extent of each of the following when it occnrs : tunica, cori)Us, 

 provascnlar strand, rib meristem, i)ith, cortex, leaf primordium, 

 axillary bud primordium, i)eripheral tissue zone (in apex of 

 gymnosperms), central tissue zone (in apex of gymnosperms), 

 initial zone. 



2. Prepare an outline di'awing of an angiospermous shoot 

 apex, filling in all the cells of the luuica and corpus zones and 



