SHOOTS OF ALGM. 



69 



not affect the shoot-nature of these kinds of structure. We have here to deal 

 simply -with flat shoots ; which by means of their chlorophyll contents, their rising 

 above the substratum, and their ability to form reproductive organs, make their 

 shoot-nature sufiBciently evident. Nothing can be more superfluous than the mor- 

 phological hair-splitting, vifhich sees in organs of this kind anything essentially 

 differerit from the leaf-shoots of other plants, simply because the external segmen- 

 tation into axis and leaf is wanting, a want which is compensated by the flat 

 extension and the abundance of chlorophyll. 



In the endless variety of forms of the Algae, any one who is accustomed to the 

 great constancy of the typical form of shoot of the vascular plants and higher Mosses, 

 is struck by the fact that here, even in closely allied subdivisions, the development 

 of shoots containing chlorophyll, so far as their segmentation into leaf and axis 

 is concerned, is extremely various. Nature, one might almost say, has here 

 given free play to the formative forces of vegetable substance, under the simpler 

 conditions of life which water presents ; while for the higher development under more 

 difficult relations, such as the life of the 

 land-plant brings with itself, the typical form 

 of leaf-shoot has evidently proved itself to 

 be most to the purpose, and with progres- 

 sive development of the vegetable kingdom 

 has been retained almost without exception. 

 Where in the Algse a sharper segmentation 

 appears, there the difference between parts 

 usually extended flat and rich in cljloro- 

 phyll, and thin stem-like parts — that is, the 

 main difference of leaves and axes — makes 

 itself evident. This occurs in a very pe- 

 culiar, and, in comparison with the vascular 

 plants and Mosses, very strange form, in 

 the Laminarise. The whole of the peren- 

 nial plant (Fig. 66) consists of a shoot 



rooted below, the lower part of which (s), like a leaf-stalk, bears at its upper 

 end % a lamina, which may be compared to a large foliage leaf. The growing 

 point of this remarkable shoot is situated at the boundary of the stalk and lamina 

 (at e) ; it produces annually, to a certain extent by intercalation, a new lamina {b'), 

 upon which the older one {b) decays away. 



Thus, although a great difference exists formally between a shoot of this 

 kind and a leaf-shoot of the higher plants, it is nevertheless clear that, by means 

 of the segmentation indicated, the same physiological advantages are attained on 

 the whole as are provided by the ordinary segmentation into leaf and axis. The 

 physiological similarity is exhibited still more in the throwing off of the flattened 

 leaf-like portion, and in the replacement of it by a new organ of a similar 

 kind. In another also highly organised genus of Algse, Sargassum, we find 

 forms of shoot which deviate but little from those of vascular plants. From 

 the growing point of a thin axis arise flat leaves {b), separated by internodes; 

 and, in addition, portions of the shoot serve as swim bladders (/), and sexual 



FIG. t<f—^archantia polymorpka (slightly magnified), 

 A B young shoots; C the two shoots, with cupules and 

 gemmfe, which arise from a gemma ; w v the depressed apical 

 region ; D a portion of epidermis seen from above ; sp stomata 

 on the rhomboid areolce (more strongly magnified). 



