270 BOTANICAL GAZETTE [ APRIt 



a palisade layer, those about the stomata being frequently elongated 

 The outer and radial walls are cuticularized and occasionally colore I. 



2. Hypoderm. — Few or many layers of isodiametric cells form the 

 tissue beneath the epicarp. The cells are somewhat thickened and 

 occasionally pitted. 



3. Outer mesocarp. — Isodiametric cells with either cellulose, or 

 sclerenchymatized and pitted, walls (stone cells, etc.) form a sharply 

 defined zone varying from a few to many cells in thickness. 



4. The middle mesocarp consists of large, usually isodiametric. 

 thin-walled cells, often turgid with a watery cell sap and containing 

 a small amount of starch. The starch grains are small, with an 

 average diameter of 10 /w. They are truncated, frequently occurrin 

 in aggregates of two and three, with slightly eccentric hilum and faint 

 rings. Polarization crosses are very distinct. 



5. Inner mesocarp. — Several layers of thin-walled cells, forming 

 this tissue, closely resemble the preceding layers. The cells are 

 small and have no visible contents. 



6. End dear p. —Very small, thin-walled, tangentially elongated cells, 

 arranged side by side in groups, form a thin transparent tissue. With 

 the exception of Cucumis, this layer remains so firmly attached to 

 the dry seed that some authors describe it as the outer layer of the 

 spermoderm. 



The anastomosing bundles occurring throughout the mesocarp an 

 bicollateral. They are either small and soft, or large and stiff, form- 

 ing a conspicuous network. The elements consist of spiral, annular. 

 and reticulated vessels, and sieve tubes having large sieve plates 

 evident without staining. 



Isolated sieve tubes and latex tubes. 20 — Fischer 5 claims there are 

 no true latex tubes, those known by this name being simply sietc 

 tubes that have ceased to function; Braemer 9 and other later 

 authors, however, use the term " latex tubes." I have seen the per- 



" According to DE Bary (Comparative anatomy of the vegetative organs oM^e 

 phanerogams and ferns i 9 8. Oxford. 1884) Dippel finds the septa and later ■ 

 of art.culated tubes provided with sieve plates and thinks them intermed.ate 

 «m tubes and latex tubes. D E Bary himself finds not the plates but pertor 

 scattered over the whole wall, and further states that there are two kinds .0 la e, 

 which do not correspond in function: (i) those secreting tannin, etc., and (2) 

 milky plants) which are closely related to sieve tubes. 





