172 de Frctine .— The Seedling Structure of certain Cactaceae. 
embryo, for the form of the seedlings corresponds very closely with that of 
the adults. A study of the seedling anatomy shows that not only the form 
but also the structure has been so influenced ; this is seen, for example, in the 
appearance of tubercles and of ‘ barrel ’ tracheides in seedlings of those plants 
in which similar features are characteristic of the adults. 
Miss Sargant has shown that much variation in the transition-phenomena 
occurs in the Liliaceae, and T. G. Hill 1 has found that ‘ the details of the 
transition in the Piperaceae are anything but rigid while there is probably 
‘ much variation in the Centrospermae ’. 
Since, then, there is such variation in small groups of plants, and since 
seedling structure can be influenced by physiological factors working on the 
adults, to me it does not appear justifiable to use such characters as indicators 
of phylogenetic connexions. 
Summary. 
Cotyledons. 
1. There is a gradual increase in succulence combined with a marked 
decrease in size in the seedlings from Pereskia , which is normally dicotyle¬ 
donous in form, through Opuntia , Nopale a, Phyllocactus , Cereus , Pilocereus , 
Echinocereus , Rhipsatis, Echinopsis , Echinocactus to Mamillaria, in which the 
seed-leaves are either microscopic or absent. 
2. In general the cotyledons are two in number ; they are always 
unequal in size, the difference being most marked in Nopalea. Seed-leaves 
are absent in Mamillaria pusilla. 
Three cotyledons were found in Opuntia stricta , Series C. In Echino¬ 
cactus Ottonis , Series i, one of the two cotyledons was split to its base, giving 
the seedling the appearance of possessing three distinct seed-leaves, and three 
cotyledonary tubercles were also present. 
In Echinocactus Ottonis , Series 3, one of the two cotyledons was bifur¬ 
cated almost to its base and the split cotyledon subtended one tubercle 
which was laterally elongated. 
3. Cotyledonary buds have been observed in Cereus triangularis, 
Echinopsis Eyriesii , E. Zuccarinii , E. Oxygona, Echinocactus bicolor , E. 
denudatus and Mamillaria hexacantha. 
There is an increase in the size of the buds, and a vascular bundle to 
supply them in Phyllocactus Hookeri , Cereus tortuosus , C. peruvianus , C. 
Jamacaru , C. Spachianus , Pilocereus exerens , P. albispinus , Echinocactus 
bicolor (one seedling), Mamillariapcntacantha and M. eriacantha. 
Tubercles with spines of the form found in the mature plant occur in 
Echinopsis multiplex , E. Lagermannii , E. tubiflora , Echinocactus Ottonis, 
1 Hill, T. G.: On the Seedling Structure ol certain Piperales. Ann. Bot., xx, 1906, p. 174. 
