. Contributions from the Botanical Laboratory and the Morris Arboretum of the University of Pennsylvania, vol. 13. Botany; Botany. Figure 15 -Tip regions of two vertical roots taken 7 feet deep in drained soil. The clusters are mycor- rhizae. Xote the paucity of permanent branches. and pointed out that, with retarded growth due to drought or other unfavorable conditions, suberization processes continue and encroach on the absorbing regions of the root. The tip ultimately may be completely enclosed by a suberized covering. •£• i u u It has been observed by various investigators, and verified by
. Contributions from the Botanical Laboratory and the Morris Arboretum of the University of Pennsylvania, vol. 13. Botany; Botany. Figure 15 -Tip regions of two vertical roots taken 7 feet deep in drained soil. The clusters are mycor- rhizae. Xote the paucity of permanent branches. and pointed out that, with retarded growth due to drought or other unfavorable conditions, suberization processes continue and encroach on the absorbing regions of the root. The tip ultimately may be completely enclosed by a suberized covering. •£• i u u It has been observed by various investigators, and verified by the writer in respect to the species studied, that the roots of pines do most of their growing in the spring and fall. Finding a growing tip was a rare occurrence in July, August, or early September. The dormant tips found generally during that period were brown and shrunken as compared with growing ones. Free-hand sections showed the cortical cells to be in a flaccid condition, and the cell walls were brown inward to the endodermis. They appeared to represent thoroughly that state described by Scott wherein the root tip is completely enclosed by a suberized covering. If it is admitted that active absorption takes place only in growing tips, and if Scott's statement is accepted that ''the distribution of suberization may be used as an indication of the delimitation or curtailment of the absorbing region of the root , then the incongruous situation is presented of absorbing area being reduced to a minimum when transpiration stresses are greatest. Scott supplies no answer to this question. Perhaps that actually is the case and the tree obtains its water during the late summer months solelv through the few vertical roots whose tips are not completely dormant. Though many of the tips found deep in the subsoil also are dormant, and the number of growing ones seenis who ly madequate to supply the needs of the tree, the fact remains that the tree passes through the dry summer pe
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