. Practical botany. Botany. ECOLOGICAL GROUPS 481 Definitely stated, some of the most noticeable characteristics often found in submerged aquatic seed plants are ^: (1) Slight development of the root system. (2) Slight development of wood cells and vessels. (3) Stiffening structures scanty or lacking. (4) Air spaces large and abundant. (5) The epidermis thin and the cuticle very thin or wanting. (6) The leaves often dissected into thread-like divisions. What are probable reasons for character- ____ istics (l)-(5) ? The thread-like divisions of the leaves mentioned in (6) are thovight to favor
. Practical botany. Botany. ECOLOGICAL GROUPS 481 Definitely stated, some of the most noticeable characteristics often found in submerged aquatic seed plants are ^: (1) Slight development of the root system. (2) Slight development of wood cells and vessels. (3) Stiffening structures scanty or lacking. (4) Air spaces large and abundant. (5) The epidermis thin and the cuticle very thin or wanting. (6) The leaves often dissected into thread-like divisions. What are probable reasons for character- ____ istics (l)-(5) ? The thread-like divisions of the leaves mentioned in (6) are thovight to favor exchange of gases between the water in which they are dissolved and the leaf interior and to offer little resistance to currents of water. 443. Characteristics of xerophytes. There are so many types of xerophytes that it is not possible in a few words to sum them up or to give the student a comprehensive idea of their peculiarities of structure and of function. Per- haps the easiest way to suggest the leading characteristics of the group is to mention a few familiar representatives of the leading types as follows: (1) The olive (Fig. 51), the rubber tree (Ficus elastica), and the wax plant (Hoya), not uncommon in greenhouses, are good examples of xerophytes with hard, thick-skinned leaves, which have a compact interior parenchyma, without the abun- dant air spaces shown in Fig. Fig. 362. A free branch and two buds of a large, common bladderwort After Beal 1 The student must not think of these characteristics as abnormal and of those of ordinary land plants as normal. It is possible that the earliest plants were aquatics and that the aquatics of to-day are more like primitive plants. But it is better to leave such reasoning for more advanced Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Berge
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