472 



LECTURE XXVIir. 



for years, and nevertheless always remains short, and only produces leaves and 

 roots, but no shoot-buds. The Ophioglossaceae and Marattiacege also behave in 

 exactly the same way, as well as the tall Tree-ferns. In all these cases the single 

 existing growing-point of the shoot of the unbranched plant, even in advanced age, 

 is the very same which was developed directly from the fertilised oosphere. Even 

 the Cycadese, so similar to the Ferns, do not as a rule become branched from the 

 growing-point, though this may occur in advanced age after the formation of 

 flowers. It occurs also occasionally as an abnormality in the otherwise so copiously 

 branched Pines that no secondary growing-points are produced from the original 

 one of the seedling, and the tree remains for many years without branching. As an 

 approximation to this, however, we may perhaps consider the case when the primary 

 shoot developed directly from the embryo grows out into a dominant main stem, the 

 lateral branches of which always grow considerably less vigorously than the stem itself, 



Fig. 310.— Apical region of a primary 

 shoot of Dictamnus Fraxinella seen from 

 above, j apex of the primary shoot ; ***the 

 young leaves; kk their axillary buds. The 

 two youngest leaves have as yet no a.\illary 

 buds. 



Fig. 311.— Bulb oi Miiscayi botry- 

 oides. One of the lower bulb-scales 

 (leaf) is turned back in order to show 

 the numerous buds situated one be- 

 side the other in its axil. 



as is the case in the Conifers and some other trees. In many species of Cactus a 

 similar condition of affairs is found in that the shoot-buds, elsewhere developed so 

 universally in the axils of the leaves of dicotyledonous plants, only rarely attain to 

 further development: here, also, the growing-point of a shoot which has once 

 attained the necessary vigour dominates the entire growth, and a lateral shoot is 

 not easily permitted to make its appearance (Cereus, Echinocachis, Mamillarid). 



In contrast to these rarer cases of the absence, or paucity of branching, however, 

 the tendency prevails in the great majority of plants to produce new growing-points 

 of shoots from the primary ones, and tertiary ones from the secondary ones ; that 

 is to develope branch-systems. In Monocotyledons and Dicotyledons it is an almost 

 universal rule within the vegetative region (that is so long as flowers are not being 

 formed) that a new growing-point of a shoot is formed in the axil of every leaf, and 

 in fact very soon after the origin of the leaf itself; this makes its appearance either 



