Further Notes on Seed Structures. 

 Fig. 4. 



143 



A 



X/£ 



xzz* 



D 



Fig. 4. Seed walls of Cycadeoidea (A and -B), Lagenostoma Lomaxi (C), 

 and Physostoma elegans (D), contrasted. 



A. — Cycadeoidea Wielandi. This seed as described is without an outer 

 fleshy or ''blow off layer," although the inner flesh and the middle scleren- 

 chyma have precisely the same development as in the other Cycadeoidea 

 seeds. 



B. — Cycadeoidea Macbridei (?), with thick blow off layer very poorly con- 

 served. The sclerenchyma layer of squarish cells with their inner basal 

 wall heavy, and the flattened inner flesh zone correspond to the outer 

 notched and inner smooth line of A. 



C. — Lagenostoma Lomaxi. Longitudinal section from above the cupule 

 showing the inner flesh and mid-sclerenchyma with peg-like projections on 

 tangential wall suggesting that an outer " blow off layer" may have failed 

 of conservation. The structure is essentially similar to that of the most 

 reduced of the Cycadeoidea seeds as shown at A, although about in propor- 

 tion to the size of the seed both flesh and sclerenchyma are much thicker. 



(Redrawn from Scott.) 



D. — Physostoma elegans. Longitudinal view of seed wall exactly showing 

 the " blow off layer" as stippled-in cells to the right, but slightly generaliz- 

 ing the complex fleshy tissues between this layer and the nucellar sac which 

 appears as a dark line to the left. Original drawing introduced to show the 

 droop of the " blow off layer" as a peculiarity also seen in Cycadeoidea. In 

 other respects interesting as a seed of ancient and complex character, 

 between which and Lagenostoma there is in actuality a much greater struc- 

 tural gap than between this latter and the Cycadeoidea seed type, although 

 the seeds of all three must be regarded as having analogous structures. 



groups of sub-epidermal cells much like the tubular cells of the 

 seed cortex or outer " enveloppe tubuleuse " and that moreover 



