Bicollateral Bundles Research Articles

An Investigation of Bidirectional Translocation in the Phloem

Patterns of (14) CO(2) , assimilate movement in Vicia jaba plants having 7 nodes were studied. Bidirectional translocation occurred throughout most of the stem length when tracer was applied to leaves of various ages. To determine whether this bidirectional translocation occurs within single sieve tubes, a O.1 % solution of the fluorescent dye K-fluorescein was applied to a lightly scraped area on the stem in the middle of a young internode. After one hour the dye was present short distances above and below the treated area. Free-hand sections of the internode showed the dye to be localized in the traces of the larger leaves below tbe treated area and in the traces of the younger leaves above the treated area. The dye was never present in the same bundle both above and below the treated area, indicating that each bundle and sieve tube translocated the dye in only one direction. These results were confirmed using Phaseolus vulgaris, Vinca rosea, and Pelargonium hortum. A similar study in which petioles of young Ecballium elaterium leaves were treated showed that usually the phloem of one bundle translocated the dye in only one direction but in some cases the external phloem of the bicollateral bundles carried the dye toward the stem while the internal phloem carried the dye toward the blade. When longer time intervals were used in all these experiments, the dye sometimes appeared in the same phloem areas both above and below the treated area. This is explained by a lateral transfer of tracer within the phloem, either through secondary phloem or through bundle anastomoses at the nodes.

Value of phloem necrosis in the diagnosis of potato leaf‐roll

In plants infected with leaf‐roll virus a type of phloem obliteration and necrosis occurs which is distinct from any abnormality produced by other pathogens or arising from physiological causes. The necrosis occurs in the primary phloem only of the bicollateral bundles. The affected tissue reacts with phloro‐glucinol in HCI. It was present in all of 179 plants of 33 varieties showing secondary leaf‐roll which were examined and was not found in any of 83 healthy plants of 20 varieties. The amount of necrosis varies in different plants. If the disease is severe, necrosis may extend to almost all parts of the plant except the stolon, tubers and roots. If the infection is mild it may be confined to a very few strands in two or three nodes near the base of the main stem. Phloem necrosis can always be found before leaf rolling is apparent.In primary leaf‐roll, slight necrosis can be found in the stem near the bases of the lowest rolled leaves and sometimes in the petioles.A technique is suggested for the use of this symptom in diagnosis.

On the internal bundles in the stem ofRumex patientia L.

The inflorescence axis ofRumex patientia has bicollateral bundles whose internal phloems give rise to obcollateral, ob-bicollateral and amphivasal bundles. Sometimes two or three internal bundles lie in association with a single outer bundle. It is concluded that the presence of such bundles is an advanced character. Farther, the condition inRheum, where the internal bundles lie detached from the outer ones, is easily derived from that inRumex.

Development and Structure of the Watermelon Seedling

1. Early stages of development of the watermelon seedling and its gross structure are described. 2. The primary root is tetrarch exarch. In transition each xylem strand is divided into two. These two divisions swing outward through arcs of 180⚬, and converge by pairs in front of the four phloem groups. When transition is completed there are four bundles composed of the four original phloem groups intact and of xylem which comes in approximately equal amounts from two adjoining groups of xylem of the original alignment. The transition is rapid and is completed at the level of the peg. 3. There is one common histogen in the primary root; all primary tissues are derived from a common meristematic region. 4. The endodermis and inner cortical layers, as well as the pericycle, of the primary root contribute to the building up of the tissues of the secondary roots. 5. There are usually six bundles in the hypocotyl: the four transition bundles and two others which are anastomosed branches from the transition bundles. All these bundles diverge into the cotyledons. 6. For a considerable period of time the cotyledons serve as photosynthetic organs. 7. The epicotyl develops slowly at first, because its vascular connections with the axis are, in the main, differentiated after germination. 8. The bicollateral bundles extend from the level at which transition is completed upward through the hypocotyl into the cotyledons and into the epicotyl. The internal phloem is derived from the parenchyma which lies adjacent to the inner faces of the bundles. It does not extend into the roots, but is connected laterally with the external phloem in the transition zone.