Characteristics of the xylem and phloem

Annual rings are absent (Fig. 1). Round groups of sieve tubes and parenchyma are present (interxylary phloem; Fig. 2). Conjunctive tissue is arranged in irregular tangential bands (Fig. 1). Vessels are small in diameter (<20 pm) and they have simple perforations (Fig. 4). Some vessels have thin helical thickenings.

Left Fig. 1. Xylem without growth zones. Groups of interxylary phloem are arranged in tangential rows. Stem of an 80 cm-high shrub, Cereus giganteus steppe, Tucson, Arizona, USA. Simmondsia chinensis, trans-

f verse section.

Fig. 4. Vessel with a simple perforation. Origin see Fig. 1, radial section.

Fibers are round and thick-walled (Fig. 4). Rays are primarely uniseriate, but some are 2-3-seriate (Fig. 3). Ray cells are typically square and upright, rarely procumbent. The phloem has a simple structure. The external part of the phel-lem contains a band of thick-walled, lignified sclereids (Fig. 5). ct

Left Fig. 1. Xylem without growth zones. Groups of interxylary phloem are arranged in tangential rows. Stem of an 80 cm-high shrub, Cereus giganteus steppe, Tucson, Arizona, USA. Simmondsia chinensis, trans-

f verse section.

Right Fig. 2. Groups of interxylary phloem cells are surrounded by a few unlignified parenchyma cells, conjunctive parenchy-matic tissue with thin-walled lignified cell walls, lignified thick-walled fibers and solitary vessels. The uniseriate rays are radially discontinuous. Origin see Fig. 1. transverse section.

Fig. 5. Simple structured phloem. The external part of the periderm (former cortex) contains a band of thick-walled, lignified sclere-ids. Origin see Fig. 1, transverse section.

Fig. 3. Rays with 1-3 cells in width. Origin see Fig. 1, tangential section.

Fig. 4. Vessel with a simple perforation. Origin see Fig. 1, radial section.

Fig. 5. Simple structured phloem. The external part of the periderm (former cortex) contains a band of thick-walled, lignified sclere-ids. Origin see Fig. 1, transverse section.

Was this article helpful?

0 0
Building Your Own Greenhouse

Building Your Own Greenhouse

You Might Just End Up Spending More Time In Planning Your Greenhouse Than Your Home Don’t Blame Us If Your Wife Gets Mad. Don't Be A Conventional Greenhouse Dreamer! Come Out Of The Mould, Build Your Own And Let Your Greenhouse Give A Better Yield Than Any Other In Town! Discover How You Can Start Your Own Greenhouse With Healthier Plants… Anytime Of The Year!

Get My Free Ebook


Post a comment