Ecological trends in the phloem and the cortex

Sclereids in the bark are much less frequent in plants in the alpine zone (4 of 35 species) than in the hill zone (33 of 88 species). It is difficult to quantify the presence of sclerenchyma since it occurs more frequent in fast- than in slow-growing individuals. Species with tangential rows of sieve-tube groups are more frequent in the alpine zone (23 of 35 species) than in the hill zone (30 of 88 species). This feature is absent in the arid zone.

Fig. 30. The phloem is characterised by distinct sieve-tube groups arranged in tangential rows, with a few sclerenchyma groups and dilatations. Bark of the root collar of a 40 cm-high biannual herb, ruderal site, mountain zone, Wyoming, USA. Berteroa incana, transverse section.

Fig. 31. Phloem with distinct sieve-tube groups arranged in tangential rows. They are compressed in external parts. A few sclerenchyma groups and dilatations occur in the cortex. Bark of the root collar of a 40 cm-high biannual herb, ruderal site, mountain zone, Switzerland. Barbarea vulgaris, transverse section.

Fig. 32. Cortex with isolated, small groups of sclerenchyma cells. The phloem contains indistinct groups of sieve tubes. Bark of the root collar of a 8 cm-high annual herb, coastal line, Cornwall, England. Coronopus didymus, transverse section.

Fig. 31. Phloem with distinct sieve-tube groups arranged in tangential rows. They are compressed in external parts. A few sclerenchyma groups and dilatations occur in the cortex. Bark of the root collar of a 40 cm-high biannual herb, ruderal site, mountain zone, Switzerland. Barbarea vulgaris, transverse section.

7 Twv

Fig. 33. Phloem with groups of sclerenchyma cells, which are arranged in tangential rows. Bark of the root collar of a 15 cm-high perennial herb, rock, hill zone, Switzerland. Arabis hirsuta, transverse section.

Fig. 34. Phloem with large radial groups of sclerenchyma which are divided by ray dilatations. Phloem of a 30 cm-high perennial herb, ruderal site, hill zone, Switzerland.

Diplotaxis tenuifolia, transverse section.

Fig. 35. Irregular, dense zone of sclerenchyma in the cortex. Phloem of a 20 cm-high annual herb, oak forest, mediterranean climate, Provence, France. Bunias erucago, 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