194 SUMMARY OF CURRENT RESEARCHES RELATING TO 



BOTANY. 



GENERAL, 



Including the Anatomy and Physiology of Seed Plants. 



Structure and Development. 

 Vegetative. 



Structure of Aloe dichotoma.* — L. Lindinger has examined the 

 structure of Aloe dichotoma, and finds that there is no distinction 

 between primary and secondary meristem, but that secondary growth 

 takes place in a double zone, consisting of one layer of thin-walled cells 

 having large cavities and a second layer of thick-walled, lignified, 

 narrow cells. Both zones are traversed by bundles. The cork-cells 

 have a strong tertiary layer of thickening. Growth in length takes 

 place in relation to a change in direction of the secondary growth in 

 thickness in the radial cells. The roots have no power of secondary 

 growth. A more general application of results shows that many of the 

 Liliiflorffi have power of secondary growth in their stems, and that 

 primary meristem develops without interruption into secondary meristem. 

 Monocotyledons, as a group, spring from tree-like forms possessing 

 power of secondary growth, and the possession of this power by certain 

 of the modern Monocotyledons, may be regarded as a mark of great 

 antiquity. The development of aerial stems, such as are found in the 

 Pandanaceaa, Velloziacere, and in different Palms and Bamboos is a 

 reversion to the ancestral type. 



Anatomy of Dioon edule.f — R. Thiessen has studied the vascular 

 anatomy of Dioon, and finds that the protostele of the embyro becomes 

 a siphonostele in the seedling, and the four protoxylem groups pass down 

 to form the protoxylem of the root. Each cotyledon contains four 

 vascular strands in direct connection with the protoxylem groups. 

 Each leaf has four vascular strands, the two central ones being derived 

 directly and without branching from" the main cylinder, while the outer 

 ones are formed by outgrowths which arise upon the opposite side of 

 the cylinder, curve round the stem in opposite directions, and so enter 

 the leaf. The cotyledonary strands are at first endarc, but gradually 

 become mesarc and finally exarc, during their upward course. The 

 same change is seen in the vascular strands of the leaf. Much of the 

 centrifugal wood in the lower part of the foliar strands is primary 

 xylem. A girdle is formed at an early stage, and is always horizontal. 



* Bot. Centralbl., xxiv. (1908) pp. 211-53 (4 pis.), 

 t Bot. Gaz., xlvi. (1908) pp. 357-80 (9 pis.). 



