6o BOTANICAL GAZETTE • [july 



trichome. The trichoblast usually divides once longitudinally, 

 SO that the trichomes are usually found in pairs (fig. g). Since almost 

 every epidermal cell gives rise to a trichoblast, the trichomes are 

 abundant and very uniformly distributed. The trichoblastic cells 

 are cut oflf as regularly in the '^ inner roots'' as in the external, but 

 of course produce trichomes only in aerial and soil roots. The 

 formation of trichoblasts in Lycopodium was first described by Nae- 

 GELi and Leitgeb (6). Leavitt (5) has described them in greater 

 detail, giving L. inundatum as an example of the type in which the 

 trichome is cut oflF by a straight anticlinal wall, and L, lucidulum as 

 an example of the type with oblique walls. The development of 

 the trichomes in L. pithyoides seems to be the same as that in L. 

 lucidulum, 



m 



The root begins to grow downward immediately after leaving 

 the stele (fig. 10), dissolving and crushing the cortex to make way 

 for its rapid enlargement. The roots bend and curve, winding in 

 and out around each other and around the leaf traces as they work 

 their way down the stem. Several roots often run side by side for a 

 considerable distance, so crowded together that the sheaths ap; ear 

 to fuse. Pritzel (7) and Strasburger both describe branching 

 as of frequent occurrence- It must be extremely rare in L. 

 pithyoides, for no cross-sections have revealed the slightest trace of 

 it, and an extensive dissection of the stem was equally unsuccessful. 

 That it docs occur is shown by a root-tip taken from an ^' inner root" 

 which has the dichotomous forking so characteristic and abundant 

 in external roots (fig. 11). It is possible that in such cases one 

 branch may become abortive owing to the crowded condition under 

 which the root is growing. 



A typical "inner root" is shown in fig. 12, On the outside is a 

 heavy sclcrenchyma sheath, which in some roots attains a thickness 

 two or three times as great. Within the sheath is a region of slightly 

 thickened parenchyma which extends to the stele. The parenchyma 

 region is the one which Strasburger erroneously called the outer- 

 most region of the root, because of the ease with which it is separated 

 from the adjoining sclcrenchyma , Bruchmann (4) in his discus- 

 sion of L. Selago corrected this error. The tearing between the two 

 regions is due not to a lack of organic connection, but to the weakness 



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